UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM N-Q

QUARTERLY SCHEDULE OF PORTFOLIO HOLDINGS OF REGISTERED
MANAGEMENT INVESTMENT COMPANY

ITEM 1.                                                     SCHEDULE OF INVESTMENTS.

WESTERN ASSET MUNICIPAL DEFINED OPPORTUNITY TRUST INC.

FORM N-Q

AUGUST 31, 2012

WESTERN ASSET MUNICIPAL DEFINED OPPORTUNITY TRUST INC.

Schedule of investments (unaudited)

August 31, 2012

See Notes to Schedule of Investments.

1

WESTERN ASSET MUNICIPAL DEFINED OPPORTUNITY TRUST INC.

Schedule of investments (unaudited) (cont’d)

August 31, 2012

See Notes to Schedule of Investments.

2

WESTERN ASSET MUNICIPAL DEFINED OPPORTUNITY TRUST INC.

Schedule of investments (unaudited) (cont’d)

August 31, 2012

See Notes to Schedule of Investments.

3

WESTERN ASSET MUNICIPAL DEFINED OPPORTUNITY TRUST INC.

Schedule of investments (unaudited) (cont’d)

August 31, 2012

Summary of Investments by Industry*

*As a percentage of total investments. Please note that Fund holdings are as of August  31, 2012 and are subject to change.

† Represents less than 0.1%.

Ratings Table*

Standard & Poor’s/Moody’s/Fitch**

* As a percentage of total investments.

** The ratings shown are based on each portfolio security’s rating as determined by Standard & Poor’s, Moody’s or Fitch, each a Nationally Recognized Statistical Rating Organization (“NRSRO”).  These ratings are the opinions of the NRSRO and are not measures of quality or guarantees of performance.  Securities may be rated by other NRSROs, and these ratings may be higher or lower. In the event that a security is rated by multiple NRSROs and receives different ratings, the Fund will treat the security as being rated in the highest rating category received from a NRSRO.

† Represents less than 0.1%.

See Notes to Schedule of Investments.

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Notes to schedule of investments (unaudited)

1. Organization and significant accounting policies

Western Asset Municipal Defined Opportunity Trust Inc. (the “Fund”) was incorporated in Maryland on January 15, 2009 and is registered as a non-diversified, closed-end management investment company under the Investment Company Act of 1940, as amended (the “1940 Act”). The Fund’s primary investment objective is to provide high current income exempt from federal income tax and then to liquidate on or about April 30, 2021 and distribute all of the Fund’s net assets to shareholders. As a secondary investment objective, the Fund will seek total return.

The following are significant accounting policies consistently followed by the Fund and are in conformity with U.S. generally accepted accounting principles (“GAAP”).

(a) Investment valuation. The valuations for fixed income securities (which may include, but are not limited to, corporate, government, municipal, mortgage-backed, collateralized mortgage obligations and asset-backed securities) and certain derivative instruments are typically the prices supplied by independent third party pricing services, which may use market prices or broker/dealer quotations or a variety of valuation techniques and methodologies. The independent third party pricing services use inputs that are observable such as issuer details, interest rates, yield curves, prepayment speeds, credit risks/spreads, default rates and quoted prices for similar securities. Short-term fixed income securities that will mature in 60 days or less are valued at amortized cost, unless it is determined that using this method would not reflect an investment’s fair value. Futures contracts are valued daily at the settlement price established by the board of trade or exchange on which they are traded. If independent third party pricing services are unable to supply prices for a portfolio investment, or if the prices supplied are deemed by the manager to be unreliable, the market price may be determined by the manager using quotations from one or more broker/dealers or at the transaction price if the security has recently been purchased and no value has yet been obtained from a pricing service or pricing broker. When reliable prices are not readily available, such as when the value of a security has been significantly affected by events after the close of the exchange or market on which the security is principally traded, but before the Fund calculates its net asset value, the Fund values these securities as determined in accordance with procedures approved by the Fund’s Board of Directors.

The Board of Directors is responsible for the valuation process and has delegated the supervision of the daily valuation process to the Legg Mason North American Fund Valuation Committee (the “Valuation Committee”). The Valuation Committee, pursuant to the policies adopted by the Board of Directors, is responsible for making fair value determinations, evaluating the effectiveness of the Fund’s pricing policies, and reporting to the Board of Directors. When determining the reliability of third party pricing information for investments owned by the Fund, the Valuation Committee, among other things, conducts due diligence reviews of pricing vendors, monitors the daily change in prices and reviews transactions among market participants.

The Valuation Committee will consider pricing methodologies it deems relevant and appropriate when making fair value determinations. Examples of possible methodologies include, but are not limited to, multiple of earnings; discount from market of a similar freely traded security; discounted cash-flow analysis; book value or a multiple thereof; risk premium/yield analysis; yield to maturity; and/or fundamental investment analysis. The Valuation Committee will also consider factors it deems relevant and appropriate in light of the facts and circumstances. Examples of possible factors include, but are not limited to, the type of security; the issuer’s financial statements; the purchase price of the security; the discount from market value of unrestricted securities of the same class at the time of purchase; analysts’ research and observations from financial institutions; information regarding any transactions or offers with respect to the security; the existence of merger proposals or tender offers affecting the security; the price and extent of public trading in similar securities of the issuer or comparable companies; and the existence of a shelf registration for restricted securities.

For each portfolio security that has been fair valued pursuant to the policies adopted by the Board of Directors, the fair value price is compared against the last available and next available market quotations. The Valuation Committee reviews the results of such back testing monthly and fair valuation occurrences are reported to the Board of Directors quarterly.

The Fund uses valuation techniques to measure fair value that are consistent with the market approach and/or income approach, depending on the type of security and the particular circumstance. The market approach uses prices and other relevant information generated by market transactions involving identical or comparable securities. The income approach uses valuation techniques to discount estimated future cash flows to present value.

GAAP establishes a disclosure hierarchy that categorizes the inputs to valuation techniques used to value assets and liabilities at measurement date. These inputs are summarized in the three broad levels listed below:

·                  Level 1—quoted prices in active markets for identical investments

·                  Level 2—other significant observable inputs (including quoted prices for similar investments, interest rates, prepayment speeds, credit risk, etc.)

5

Notes to schedule of investments (unaudited) (continued)

·                  Level 3—significant unobservable inputs (including the Fund’s own assumptions in determining the fair value of investments)

The inputs or methodologies used to value securities are not necessarily an indication of the risk associated with investing in those securities.

The following is a summary of the inputs used in valuing the Fund’s assets and liabilities carried at fair value:

†See Schedule of Investments for additional detailed categorizations.

(b) Futures contracts. The Fund uses futures contracts generally to gain exposure to, or hedge against, changes in interest rates or gain exposure to, or hedge against, changes in certain asset classes. A futures contract represents a commitment for the future purchase or sale of an asset at a specified price on a specified date.

Upon entering into a futures contract, the Fund is required to deposit cash or cash equivalents with a broker in an amount equal to a certain percentage of the contract amount. This is known as the “initial margin” and subsequent payments (“variation margin”) are made or received by the Fund each day, depending on the daily fluctuation in the value of the contract.

Futures contracts involve, to varying degrees, risk of loss. In addition, there is the risk that the Fund may not be able to enter into a closing transaction because of an illiquid secondary market.

(c) Security transactions. Security transactions are accounted for on a trade date basis.

2. Investments

At August 31, 2012, the aggregate gross unrealized appreciation and depreciation of investments for federal income tax purposes were substantially as follows:

At August 31, 2012, the Fund had the following open futures contracts:

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Notes to schedule of investments (unaudited) (continued)

3. Derivative instruments and hedging activities

Financial Accounting Standards Board Codification Topic 815 requires enhanced disclosure about an entity’s derivative and hedging activities.

The following is a summary of the Fund’s derivative instruments categorized by risk exposure at August 31, 2012.

During the period ended August 31, 2012, the volume of derivative activity for the Fund was as follows:

4. Recent accounting pronouncement

In May 2011, the Financial Accounting Standards Board issued Accounting Standards Update No. 2011-04, Fair Value Measurement (Topic 820) - Amendments to Achieve Common Fair Value Measurement and Disclosure Requirements in U.S. GAAP and IFRSs (“ASU No. 2011-04”). ASU No. 2011-04 establishes common requirements for measuring fair value and for disclosing information about fair value measurements. ASU No. 2011-04 is effective during interim and annual periods beginning after December 15, 2011. Management has evaluated ASU No. 2011-04 and concluded that it does not materially impact the financial statement amounts; however, as required, additional disclosure has been included about fair value measurement.

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

Western Asset Municipal Defined Opportunity Trust Inc.

Date:  October 26, 2012

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of the registrant and in the capacities and on the dates indicated.

Date:  October 26, 2012

Date:  October 26, 2012