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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
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MIC-Info: RSA-MD5,RSA,
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 h1otgiKp1fAB8lz/gLNQxA==

<SEC-DOCUMENT>0001179110-10-004589.txt : 20100305
<SEC-HEADER>0001179110-10-004589.hdr.sgml : 20100305
<ACCEPTANCE-DATETIME>20100305152524
ACCESSION NUMBER:		0001179110-10-004589
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100304
FILED AS OF DATE:		20100305
DATE AS OF CHANGE:		20100305

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			RIFFE STEPHEN EDWARD
		CENTRAL INDEX KEY:			0001221658

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14023
		FILM NUMBER:		10660493

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			CORPORATE OFFICE PROPERTIES TRUST
		CENTRAL INDEX KEY:			0000860546
		STANDARD INDUSTRIAL CLASSIFICATION:	REAL ESTATE INVESTMENT TRUSTS [6798]
		IRS NUMBER:				232947217
		STATE OF INCORPORATION:			MD
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		6711 COLUMBIA GATEWAY DRIVE
		STREET 2:		SUITE 300
		CITY:			COLUMBIA
		STATE:			MD
		ZIP:			21046
		BUSINESS PHONE:		4432855400

	MAIL ADDRESS:	
		STREET 1:		6711 COLUMBIA GATEWAY DRIVE
		STREET 2:		SUITE 300
		CITY:			COLUMBIA
		STATE:			MD
		ZIP:			21046

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	CORPORATE OFFICE PROPERTIES TRUST INC
		DATE OF NAME CHANGE:	19980105

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ROYALE INVESTMENTS INC
		DATE OF NAME CHANGE:	19930328

	FORMER COMPANY:	
		FORMER CONFORMED NAME:	ROYALE REIT INC
		DATE OF NAME CHANGE:	19600201
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-03-04</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000860546</issuerCik>
        <issuerName>CORPORATE OFFICE PROPERTIES TRUST</issuerName>
        <issuerTradingSymbol>OFC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001221658</rptOwnerCik>
            <rptOwnerName>RIFFE STEPHEN EDWARD</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2410 STRYKER AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>VIENNA</rptOwnerCity>
            <rptOwnerState>VA</rptOwnerState>
            <rptOwnerZipCode>22181</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>EVP and CFO</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Shares</value>
            </securityTitle>
            <transactionDate>
                <value>2010-03-04</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>15856</value>
                </transactionShares>
                <transactionPricePerShare>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>115960</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">3-4-2010-Restricted shares shall vest equally over a three year period, with the first vesting on the first anniversary of the grant date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Stephen E. Riffee</signatureName>
        <signatureDate>2010-03-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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