<SEC-DOCUMENT>0001179110-13-014277.txt : 20130917
<SEC-HEADER>0001179110-13-014277.hdr.sgml : 20130917
<ACCEPTANCE-DATETIME>20130917160254
ACCESSION NUMBER:		0001179110-13-014277
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20130913
FILED AS OF DATE:		20130917
DATE AS OF CHANGE:		20130917

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

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			HAMLIN CLAY W III
		CENTRAL INDEX KEY:			0001048456

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14023
		FILM NUMBER:		131101327

	MAIL ADDRESS:	
		STREET 1:		THE SHIDLER GROUP PHILADELPHIA
		STREET 2:		ONE LOGAN SQUARE SUITE 1105
		CITY:			PHILADELPHIA
		STATE:			PA
		ZIP:			19103
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-09-13</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001048456</rptOwnerCik>
            <rptOwnerName>HAMLIN CLAY W III</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>6711 COLUMBIA GATEWAY DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 300</rptOwnerStreet2>
            <rptOwnerCity>COLUMBIA</rptOwnerCity>
            <rptOwnerState>MD</rptOwnerState>
            <rptOwnerZipCode>21046</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Shares of COPT</value>
            </securityTitle>
            <transactionDate>
                <value>2013-09-13</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>1000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23.328</value>
                    <footnoteId id="F2"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>11390</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">The reporting person's purchase of one thousand (1,000) COPT common shares reported herein was matchable under Section 16(b) of the Securities Exchange Act of 1934 with the sale by LBCW Limited Partnership (the &quot;Partnership&quot;) of ten thousand (10,000) COPT common shares on May 1, 2013 at a price of $28.8647 per share on May 1, 2013. The reporting person has an indirect beneficial ownership interest in the shares held by the Partnership.  The reporting person has agreed to pay to COPT $5,635.40, representing the full amount of the profit realized in connection with the short-swing transaction.</footnote>
        <footnote id="F2">This price is an average with purchases between $23.328 and $23.329 per share.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Karen M. Singer, by Power of Attorney</signatureName>
        <signatureDate>2013-09-16</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
