UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED
MANAGEMENT INVESTMENT COMPANIES

ITEM 1.                  REPORT TO STOCKHOLDERS.

The Annual Report to Stockholders is filed herewith.

Annual Report

Western Asset Investment Grade Defined Opportunity Trust Inc.
(IGI)

Fund objectives

The Fund’s primary investment objective is to provide current income and then to liquidate and distribute substantially all of the Fund’s net assets to stockholders on or about December 2, 2024. As a secondary investment objective, the Fund will seek capital appreciation. There can be no assurance the Fund will achieve its investment objectives.

What’s inside

Dear Shareholder,

We are pleased to provide the annual report of Western Asset Investment Grade Defined Opportunity Trust Inc. for the twelve-month reporting period ended November 30, 2010. Please read on for a detailed look at prevailing economic and market conditions during the Fund’s reporting period and to learn how those conditions have affected Fund performance.

As always, we remain committed to providing you with excellent service and a full spectrum of investment choices. We also remain committed to supplementing the support you receive from your financial advisor. One way we accomplish this is through our website, www.leggmason.com/cef. Here you can gain immediate access to market and investment information, including:

·                  Fund prices and performance,

·                  Market insights and commentaries from our portfolio managers, and

·                  A host of educational resources.

We look forward to helping you meet your financial goals.

Sincerely,

R. Jay Gerken, CFA

Chairman, President and Chief Executive Officer

December 31, 2010

Investment commentary

Economic review

While the U.S. economy continued to expand over the twelve months ended November 30, 2010, economic data was mixed and unemployment remained elevated. The Federal Reserve Board (“Fed”)i expressed concerns regarding the direction of the economy and took additional actions in an attempt to spur growth. This initially caused investor sentiment to improve, but the financial markets declined toward the end of the reporting period given a re-escalation of the European sovereign debt crisis.

In September 2010, the National Bureau of Economic Research (“NBER”), the organization charged with determining when recessions start and end, announced that the recession that began in December 2007 had concluded in June 2009. However, the NBER said, “In determining that a trough occurred in June 2009, the committee did not conclude that economic conditions since that month have been favorable or that the economy has returned to operating at normal capacity.” The NBER’s point is well-taken given continued areas of weakness in the U.S. economy.

Although the U.S. Department of Commerce continued to report positive U.S. gross domestic product (“GDP”)ii growth, the expansion has moderated since peaking at 5.0% in the fourth quarter of 2009. A slower drawdown in business inventories and renewed consumer spending were contributing factors spurring the economy’s solid growth at the end of 2009. However, the economy has grown at a more modest pace thus far in 2010. According to the Commerce Department, GDP growth was 3.7% and 1.7% during the first and second quarters of 2010, respectively. GDP growth then edged somewhat higher to 2.6% in the third quarter.

Turning to the job market, after experiencing sharp job losses in 2009, the U.S. Department of Labor reported that over one million new positions were added during the first five months of 2010. Included in that number, however, were 700,000 temporary government jobs tied to the 2010 Census. From June through September, more than 525,000 of these temporary positions were eliminated. This more than offset private sector growth and resulted in a total net loss of 300,000 jobs from June through September. The employment picture then brightened somewhat in October, as 172,000 new jobs were created. Payrolls then increased a disappointing 39,000 in November and the unemployment rate inched up to end the period at 9.8%. The unemployment rate has now exceeded 9.0% since May 2009.

There was mixed news in the housing market during the period. According to the National Association of Realtors (“NAR”), existing-home sales increased 7.0% and 8.0% in March and April, respectively, after sales had fallen for the period from December 2009 through February 2010. The rebound was largely attributed to people rushing to take advantage of the government’s $8,000 tax credit for first-time home buyers that expired at the end of April. However, with the end of the tax credit, existing-home sales then declined from May through July. Sales then rose 7.3% and 10.0% in August and September, respectively. Sales then dipped 2.2% in October and rose 5.6% in November. Looking at home prices, the NAR reported that the median existing-home price for all housing types was $170,600 in November 2010, which was 0.4% higher than in November 2009. Prices appeared to stabilize somewhat as the number of existing homes on the market declined in November. The inventory of unsold

Investment commentary (cont’d)

homes was a 9.5 month supply in November at the current sales level, versus a 10.5 month supply in October.

One overall bright spot for the economy has been the manufacturing sector. Based on the Institute for Supply Management’s PMIiii, the manufacturing sector has grown sixteen consecutive months since it began expanding in August 2009. After reaching a six-year peak of 60.4 in April 2010, PMI data indicated somewhat more modest growth from May through July (a reading below 50 indicates a contraction, whereas a reading above 50 indicates an expansion). The manufacturing sector then expanded at a faster pace in August, before moderating somewhat in September. Manufacturing then grew in October at its fastest pace since May with a reading of 56.9 for the month, before dipping to 56.6 in November.

Financial market overview

During the majority of the reporting period, the financial markets were largely characterized by healthy investor risk appetite and solid results by lower-quality bonds. However, the market experienced a sharp sell-off in late April and in May, during which risk aversion returned and investors flocked to the relative safety of U.S. Treasury securities. Demand for riskier assets then resumed in June and July, followed by another “flight to quality” in August. Risk appetite then returned in September and October before the financial markets again weakened beginning in mid-November.

Due to signs that economic growth was slowing toward the end of the reporting period, the Fed took further actions to spur the economy. At its August 10th meeting, the Fed announced an ongoing program that calls for using the proceeds from expiring agency debt and agency mortgage-backed securities to purchase longer-dated Treasury securities.

In addition, the Fed remained cautious throughout the reporting period given pockets of weakness in the economy. At its meeting in September 2010, the Fed said, “The Committee will continue to monitor the economic outlook and financial developments and is prepared to provide additional accommodation if needed to support the economic recovery. . . .” This led to speculation that the Fed may again move to purchase large amounts of agency and Treasury securities in an attempt to avoid a double-dip recession and ward off deflation.

The Fed then took additional action in early November. Citing that “the pace of recovery in output and employment continues to be slow,” the Fed announced another round of quantitative easing to help stimulate the economy, entailing the purchase of $600 billion of long-term U.S. Treasury securities by the end of the second quarter of 2011. This, coupled with the Fed’s previously announced program to use the proceeds of expiring securities to purchase Treasuries, means it could buy a total of $850 billion to $900 billion of Treasury securities by the end of June 2011.

Fixed-income market review

Continuing the trend that began in the second quarter of 2009, nearly every spread sector (non-Treasury) outperformed equal-durationiv Treasuries during most of the first half of the reporting period. Over that time, investor confidence was high given encouraging economic data, continued low interest rates, benign inflation and rebounding corporate profits. Robust investor

appetite was then replaced with heightened risk aversion toward the end of April and during the month of May. This was due to the escalating sovereign debt crisis in Europe, uncertainties regarding new financial reforms in the U.S. and some worse-than-expected economic data. Most spread sectors then produced positive absolute returns in June and July, as investor demand for these securities again increased. There was another bout of risk aversion in August, given fears that the economy may slip back into a recession. However, with the Fed indicating the possibility of another round of quantitative easing, most spread sectors rallied in September and October. The spread sectors then ended the reporting period on a weak note as financial troubles in Ireland resulted in a re-emergence of the European sovereign debt crisis.

Both short- and long-term Treasury yields fluctuated but, overall, moved lower during the twelve months ended November 30, 2010. When the period began, two- and ten-year Treasury yields were 0.67% and 3.21%, respectively. On April 5, 2010, two- and ten-year Treasury yields peaked at 1.18% and 4.01%, respectively. Subsequent to hitting their highs for the period, yields largely declined during much of the remainder of the reporting period. When the period ended on November 30, 2010, two-year Treasury yields were 0.45%, versus a low of 0.33% earlier in the month. Ten-year Treasury yields ended the period at 2.81%, which was higher than their trough of 2.41% that occurred in October. Longer-term yields moved higher toward the end of the period as fears of future inflation increased in light of the Fed’s additional policy accommodation. For the twelve months ended November 30, 2010, the Barclays Capital U.S. Aggregate Indexv returned 6.02%.

The U.S. high-yield bond market produced strong results during the reporting period. The asset class posted positive returns during each month, except for May and November 2010 when risk aversion rose sharply. The high-yield market was supported by better-than-expected corporate profits and overall strong investor demand. All told, the Barclays Capital U.S. High Yield — 2% Issuer Cap Indexvi returned 16.60% for the twelve months ended November 30, 2010.

Emerging market debt prices rallied over the reporting period, also posting positive returns each month during the period except for May and November 2010. This solid performance was triggered by strong economic growth in many emerging market countries, solid domestic demand and generally robust investor demand for the asset class. The JPMorgan Emerging Markets Bond Index Global (“EMBI Global”)vii returned 12.77% over the twelve months ended November 30, 2010.

As always, thank you for your confidence in our stewardship of your assets.

Sincerely,

R. Jay Gerken, CFA

Chairman, President and Chief Executive Officer

December 31, 2010

All investments are subject to risk including the possible loss of principal. Past performance is no guarantee of future results. All index performance reflects no deduction for fees, expenses or taxes. Please note that an investor cannot invest directly in an index.

Investment commentary (cont’d)

Fund overview

Q. What is the Fund’s investment strategy?

A. The Fund’s primary investment objective is to provide current income and then to liquidate and distribute substantially all of the Fund’s net assets to stockholders on or about December 2, 2024. As a secondary investment objective, the Fund will seek capital appreciation. There can be no assurance the Fund will achieve its investment objectives.

The Fund seeks to achieve its investment objectives by investing, under normal market conditions, at least 80% of its net assets in investment grade corporate fixed-income securities of varying maturities. The Fund may invest up to 20% of its net assets in corporate fixed-income securities of below investment grade quality at the time of investment and other securities, including obligations of the U.S. government, its agencies or instrumentalities, common stocks, warrants and depositary receipts. While the Fund may invest up to 20% of its net assets in below investment grade securities, the Fund will, under normal market conditions, maintain a portfolio with an overall dollar-weighted average of investment grade credit quality. The Fund may invest up to 20% of its net assets in securities of foreign issuers located anywhere in the world, including issuers located in emerging market countries. Additionally, the Fund may invest up to 20% of its net assets in non-U.S. dollar denominated securities.

The Fund may invest in derivative instruments, such as options contracts, futures contracts, options on futures contracts, indexed securities, credit default swaps and other swap agreements, provided that the Fund’s exposure to derivative instruments, as measured by the total notional amount of all such instruments, will not exceed 20% of its net assets.

In purchasing securities and other investments for the Fund, we may take full advantage of the entire range of maturities and durationsi offered by corporate fixed-income securities and may adjust the average maturity or duration of the Fund’s portfolio from time to time, depending on our assessment of the relative yields available on securities of different maturities and durations and our expectations of future changes in interest rates.

The Fund may take on leveraging risk by utilizing certain management techniques, whereby it will segregate liquid assets, enter into offsetting transactions or own positions covering its obligations. To the extent the Fund covers its commitment under such a portfolio management technique, such instrument will not be considered a senior security for the purposes of the Investment Company Act of 1940. However, as a fundamental policy, the Fund will not leverage its capital structure by issuing senior securities such as preferred shares or debt instruments.

At Western Asset Management Company (“Western Asset”), the Fund’s subadviser, we utilize a fixed-income team approach, with decisions derived from interaction among various investment management sector specialists. The sector teams are comprised of Western Asset’s senior portfolio managers, research analysts and an in-house economist. Under this team approach, management of client fixed-income portfolios will reflect a consensus of interdisciplinary views within the Western Asset organization. The portfolio managers responsible for development of investment strategy, day-to-day portfolio management, oversight and coordination of the Fund are Stephen A. Walsh, Michael C. Buchanan, Timothy J. Settel, Dipankar Shewaram and Ryan K. Brist.

Fund overview (cont’d)

Q. What were the overall market conditions during the Fund’s reporting period?

A. During the twelve months ended November 30, 2010, the riskier segments of the fixed-income market produced strong results and outperformed U.S. Treasuries. This was due, in part, to improving economic conditions following the lengthy downturn from mid-2008 through mid-2009. Also supporting the spread sectors (non-U.S. Treasuries) was overall solid demand from investors seeking incremental yields given the low rates available from short-term fixed-income securities.

The spread sectors rallied during most of the reporting period, with notable exceptions being in late April and May 2010, as well as August and November 2010. Starting toward the end of April, there was a “flight to quality,” triggered by concerns regarding the escalating sovereign debt crisis in Europe. In addition, investor sentiment was negatively impacted by uncertainties surrounding financial reform legislation in the U.S. and signs that economic growth was moderating. Collectively, this caused investors to flock to the relative safety of Treasury securities, driving their yields lower and prices higher.

Robust investor risk appetite largely resumed during June and July, and again in September and October. These turnarounds occurred as the situation in Europe appeared to stabilize, the financial reform bill was signed into law and the Federal Reserve Board (“Fed”)ii continued to indicate that it would keep short-term rates low for an extended period. However, investor risk aversion returned in November when fears regarding the European debt crisis re-emerged.

The yields on two- and ten-year Treasuries began the fiscal year at 0.67% and 3.21%, respectively. Treasury yields fluctuated during the twelve-month reporting period given changing perceptions regarding the economy, interest rates, inflation and deflation. Yields moved sharply lower in October 2010 in anticipation of additional quantitative easing by the Fed. Yields then reversed course toward the end of the period as certain economic data were stronger than expected and there were concerns regarding future inflation. During the fiscal year, two-year Treasury yields moved as high as 1.18% and as low as 0.33%, whereas ten-year Treasuries rose as high as 4.01% and as low as 2.41%. On November 30, 2010, yields on two- and ten-year Treasuries were 0.45% and 2.81%, respectively.

All told, the Barclays Capital U.S. Aggregate Indexiii and the Barclays Capital U.S. Credit Indexiv returned 6.02% and 8.48%, respectively, for the twelve months ended November 30, 2010.

Q. How did we respond to these changing market conditions?

A. A number of adjustments were made to the Fund’s portfolio during the reporting period. We increased the Fund’s exposure to the Financials sector and, in particular, banks. This was based on our expectation for improving profits in the banking industry. We also participated in the new issuance market by selectively purchasing both investment grade and high-yield corporate bonds from a variety of sectors. While the Fund maintained its lower-quality bias versus the benchmark, we pared our exposure to certain lower-quality securities to capture profits toward the end of the fiscal year.

The Fund employed U.S. Treasury futures during the reporting period to

manage duration. This strategy detracted from the Fund’s performance.

Performance review

For the twelve months ended November 30, 2010, Western Asset Investment Grade Defined Opportunity Trust Inc. returned 10.28% based on its net asset value (“NAV”)v and 12.52% based on its New York Stock Exchange (“NYSE”) market price per share. The Fund’s unmanaged benchmark, the Barclays Capital U.S. Credit Index, returned 8.48% for the same period. The Lipper Corporate Debt BBB-Rated Closed-End Funds Category Averagevi returned 13.46% over the same time frame. Please note that Lipper performance returns are based on each fund’s NAV.

During the twelve-month period, the Fund made distributions to shareholders totaling $1.25 per share. The performance table shows the Fund’s twelve-month total return based on its NAV and market price as of November 30, 2010. Past performance is no guarantee of future results.

Performance Snapshot as of November 30, 2010

All figures represent past performance and are not a guarantee of future results.

*      Total returns are based on changes in NAV or market price, respectively. Total returns assume the reinvestment of all distributions in additional shares in accordance with the Fund’s Dividend Reinvestment Plan.

Q. What were the leading contributors to performance?

A. The largest contributor to the Fund’s relative performance during the reporting period was its lower-quality bias. This positioning was beneficial given strong demand from investors looking to generate incremental yield. During the reporting period, the Fund maintained roughly a 15% total allocation to below investment grade credit (high-yield bonds and floating rate senior secured high-yield loans). Within the investment grade market, we maintained an overweight versus the benchmark to lower-rated BBB bonds which outperformed the overall benchmark during the period. In addition, we underweighted bonds rated AAA, AA and A which underperformed the benchmark.

Issue selection also significantly contributed to results. Within the high-yield market, overweight positions in Sprint Capital Corp. and AIG’s aircraft leasing arm, International Lease Finance Corp. were rewarded. Wireless service provider Sprint posted improved fundamental results and continued to generate significant free cash flow, which caused its BB-rated unsecured bonds to perform well during the period. As we anticipated, AIG’s International Lease Finance freed up collateral by repaying a government loan during the period and the company accessed the capital markets in order to extend its maturity profile. This balance sheet management, combined with stable fundamental results, caused the issuer’s bonds to rally significantly during the period.

Among the Fund’s best performers within the investment grade market were overweight positions in Williams Cos. Inc. and Altria Group Inc. Williams Cos. is an energy company whose core business includes natural gas exploration and production (“E&P”) and natural gas processing and transportation via its majority stakeholding in Williams

Fund overview (cont’d)

Partners LP. Williams Cos. performed well as its pipeline business continued to generate strong cash flows with the distributions reinvested into the E&P operations to fund growth. Company management remains focused on preserving liquidity which was seen as beneficial for debt holders. Tobacco company Altria Group continued to generate fundamental results that were in line with expectations. We believe Altria has a strong management team which has done an effective job of offsetting declining cigarette volumes by taking market share with its premium brands and growing its smokeless tobacco division. Additionally, Altria reduced its pension obligations in 2010 which helped its BBB-rated corporate bonds to rally significantly during the reporting period.

Sector allocation was, overall, also a positive for the Fund’s performance. In particular, having an underweight to non-corporates (primarily sovereign and Build America Bonds) was a contributor given their underperformance versus corporate credit during the fiscal year. Elsewhere, the Fund’s overweight to Financials boosted results as the sector outperformed the overall benchmark.

Q. What were the leading detractors from performance?

A. The largest detractors from relative performance during the reporting period were several individual securities. Our first lien secured exposure to high-yield issuer Blockbuster Inc. was a negative for performance. Poor fundamental results and concerns over Blockbuster’s in-store rental model pressured its bonds during the period. In September 2010, the company filed for bankruptcy. As a result, our holdings detracted from performance as their prices declined in a rising market. We liquidated our position during the period. Elsewhere, an overweight in Telecom Italia Capital SA was not rewarded as its bonds did not rally in a rising market based on investor concerns that the sovereign debt crisis in Greece and Ireland might spread to Italy. We continue to hold our Telecom Italia position based on predictable fundamental performance in this defensive sector, and we feel the additional compensation of roughly 175 basis points (1.75%) versus other BBB-rated corporate bonds is attractive. At the end of the reporting period, Telecom Italia traded close to where we acquired the position.

While the Fund’s sector allocation was a positive for results overall, an underweight to Consumer Cyclicals1 was a modest detractor based on the sector’s slight outperformance versus the benchmark during the reporting period.

Looking for additional information?

The Fund is traded under the symbol “IGI” and its closing market price is available in most newspapers under the NYSE listings. The daily NAV is available on-line under the symbol “XIGIX” on most financial websites. Barron’s and the Wall Street Journal’s Monday edition both carry closed-end fund tables that provide additional information. In addition, the Fund issues a quarterly press release that can be found on most major financial websites as well as www.leggmason.com/cef.

In a continuing effort to provide information concerning the Fund, shareholders may call 1-888-777-0102 (toll free), Monday through Friday from 8:00 a.m. to 5:30 p.m. Eastern Time, for the Fund’s current NAV, market price and other information.

Thank you for your investment in Western Asset Investment Grade Defined Opportunity Trust Inc. As always, we appreciate that you have chosen us to manage your assets and we remain focused on achieving the Fund’s investment goals.

Sincerely,

Western Asset Management Company

December 21, 2010

RISKS: The Fund’s investments are subject to credit risk, inflation risk and interest rate risk. As interest rates rise, bond prices fall, reducing the value of the Fund’s holdings. The Fund may invest in lower-rated high-yield bonds which are subject to grater credit risk (risk of default) than higher-rated obligations. The Fund may use derivatives, such as options and futures, which can be illiquid, may disproportionately increase losses and have a potentially large impact on Fund performance. The Fund may invest in securities or engage in transactions that have the economic effects of leverage which can increase the risk and volatility of the Fund.

Portfolio holdings and breakdowns are as of November 30, 2010 and are subject to change and may not be representative of the portfolio managers’ current or future investments. Please refer to pages 9 through 19 for a list and percentage breakdown of the Fund’s holdings.

The mention of sector breakdowns is for informational purposes only and should not be construed as a recommendation to purchase or sell any securities. The information provided regarding such sectors is not a sufficient basis upon which to make an investment decision. Investors seeking financial advice regarding the appropriateness of investing in any securities or investment strategies discussed should consult their financial professional. The Fund’s top five sector holdings (as a percentage of net assets) as of November 30, 2010 were: Financials (33.2%), Energy (11.1%), Consumer Discretionary (10.4%), Telecommunication Services (9.5%) and Utilities (7.4%). The Fund’s portfolio composition is subject to change at any time.

All investments are subject to risk including the possible loss of principal. Past performance is no guarantee of future results. All index performance reflects no deduction for fees, expenses or taxes. Please note that an investor cannot invest directly in an index.

The information provided is not intended to be a forecast of future events, a guarantee of future results or investment advice. Views expressed may differ from those of the firm as a whole.

Fund at a glance† (unaudited)

Investment breakdown (%) as a percent of total investments

Spread duration (unaudited)

Economic Exposure — November 30, 2010

Spread duration measures the sensitivity to changes in spreads. The spread over Treasuries is the annual risk-premium demanded by investors to hold non-Treasury securities. Spread duration is quantified as the % change in price resulting from a 100 basis points change in spreads. For a security with positive spread duration, an increase in spreads would result in a price decline and a decline in spreads would result in a price increase. This chart highlights the market sector exposure of the Fund’s portfolio and the exposure relative to the selected benchmark as of the end of the reporting period.

Effective duration (unaudited)

Interest Rate Exposure — November 30, 2010

Effective duration measures the sensitivity to changes in Treasury yields. Effective duration is quantified as the % change in price resulting from a 100 basis points change in Treasury yields. For a security with positive effective duration, an increase in Treasury yields would result in a price decline and a decline in Treasury yields would result in a price increase. This chart highlights the interest rate exposure of the Fund’s portfolio relative to the selected benchmark as of the end of the reporting period.

Schedule of investments

November 30, 2010

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Schedule of investments (cont’d)

November 30, 2010

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Schedule of investments (cont’d)

November 30, 2010

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Western Asset Investment Grade Defined Opportunity Trust Inc.

See Notes to Financial Statements.

Schedule of investments (cont’d)

November 30, 2010

Western Asset Investment Grade Defined Opportunity Trust Inc.