<SEC-DOCUMENT>0001140361-12-043783.txt : 20121015
<SEC-HEADER>0001140361-12-043783.hdr.sgml : 20121015
<ACCEPTANCE-DATETIME>20121015164721
ACCESSION NUMBER:		0001140361-12-043783
CONFORMED SUBMISSION TYPE:	3
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20121005
FILED AS OF DATE:		20121015
DATE AS OF CHANGE:		20121015

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:			APG Asset Management US Inc.
		CENTRAL INDEX KEY:			0001323255
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14023
		FILM NUMBER:		121144250

	BUSINESS ADDRESS:	
		STREET 1:		666 THIRD AVENUE
		STREET 2:		2ND FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10017
		BUSINESS PHONE:		(917) 368-3500

	MAIL ADDRESS:	
		STREET 1:		666 THIRD AVENUE
		STREET 2:		2ND FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10017

	FORMER NAME:	
		FORMER CONFORMED NAME:	APG Investments US Inc.
		DATE OF NAME CHANGE:	20080509

	FORMER NAME:	
		FORMER CONFORMED NAME:	ABP Investments US, Inc.
		DATE OF NAME CHANGE:	20050407

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			APG All Pensions Group NV
		CENTRAL INDEX KEY:			0001434819
		STATE OF INCORPORATION:			P7
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14023
		FILM NUMBER:		121144249

	BUSINESS ADDRESS:	
		STREET 1:		OUDE LINDESTRAAT 70
		STREET 2:		POSTBUS 6401
		CITY:			HEERLEN
		STATE:			P7
		ZIP:			00000
		BUSINESS PHONE:		917-368-3500

	MAIL ADDRESS:	
		STREET 1:		APG ASSET MANAGEMENT US INC.
		STREET 2:		666 3RD AVE, 2ND FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10017

	FORMER NAME:	
		FORMER CONFORMED NAME:	APG Asset Management NV
		DATE OF NAME CHANGE:	20090309

	FORMER NAME:	
		FORMER CONFORMED NAME:	APG All Pensions Group
		DATE OF NAME CHANGE:	20080512

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			APG Group
		CENTRAL INDEX KEY:			0001434820
		STATE OF INCORPORATION:			P7
		FISCAL YEAR END:			1231

	FILING VALUES:
		FORM TYPE:		3
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-14023
		FILM NUMBER:		121144251

	BUSINESS ADDRESS:	
		STREET 1:		OUDE LINDESTRAAT 70
		STREET 2:		POSTBUS 6401
		CITY:			HEERLEN
		STATE:			P7
		ZIP:			00000
		BUSINESS PHONE:		917-368-3500

	MAIL ADDRESS:	
		STREET 1:		APG INVESTMENTS US INC.
		STREET 2:		666 3RD AVE, 2ND FLOOR
		CITY:			NEW YORK
		STATE:			NY
		ZIP:			10017
</SEC-HEADER>
<DOCUMENT>
<TYPE>3
<SEQUENCE>1
<FILENAME>doc1.xml
<DESCRIPTION>FORM 3
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0206</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2012-10-05</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001323255</rptOwnerCik>
            <rptOwnerName>APG Asset Management US Inc.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>666 THIRD AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2>SECOND FLOOR</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10017</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001434820</rptOwnerCik>
            <rptOwnerName>APG Group</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>OUDE LINDESTRAAT 70</rptOwnerStreet1>
            <rptOwnerStreet2>POSTBUS 6401</rptOwnerStreet2>
            <rptOwnerCity>HEERLEN</rptOwnerCity>
            <rptOwnerState>P7</rptOwnerState>
            <rptOwnerZipCode>00000</rptOwnerZipCode>
            <rptOwnerStateDescription>NETHERLANDS</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Parent Company</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001434819</rptOwnerCik>
            <rptOwnerName>APG All Pensions Group NV</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>GUSTAV MAHLERPLEIN 3</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>1082 MS AMSTERDAM</rptOwnerCity>
            <rptOwnerState>P7</rptOwnerState>
            <rptOwnerZipCode>00000</rptOwnerZipCode>
            <rptOwnerStateDescription>NETHERLANDS</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>Parent Company</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Corporate Office Properties Trust (OFC)</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes></footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Ludmila Chwazik</signatureName>
        <signatureDate>2012-10-15</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
