<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2006-05-11</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000037008</issuerCik>
        <issuerName>Winthrop Realty Trust</issuerName>
        <issuerTradingSymbol>FUR</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001214344</rptOwnerCik>
            <rptOwnerName>BERKOWITZ BRUCE R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1></rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity></rptOwnerCity>
            <rptOwnerState></rptOwnerState>
            <rptOwnerZipCode></rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Shares of Beneficial Interest</value>
            </securityTitle>
            <transactionDate>
                <value>2006-05-11</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>288491</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>5.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1620617</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>see</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">195,866 shares acquired directly from Issuer in connection with exercise of over-allotment subscription option in Issuer's recently completed rights offering and 92,625 shares acquired from FUR Investors LLC in a private transaction.</footnote>
        <footnote id="F2">Amount consists of (i) 42,122 common shares owned directly by Mr. Berkowitz, (ii) 1,053,036 common shares owned by Fairholme Ventures II, LLC, an entity in which Fairholme Capital Management is the managing member, (iii) 16,168 common shares owned by Fairholme Holdings Ltd., the investment manager of which Fairholme Capital Management, LLC and (iv) 509,291 owned by Fairholme Associates, L.P., an entity in which Fairholme Capital Management, LLC is the general partner. Mr. Berkowitz is managing member of Fairholme Capital Management, LLC.</footnote>
        <footnote id="F3">In addition to the foregoing, Fairholme Ventures II, LLC holds 400,000 of the Issuer's Series B-1 Preferred Shares which are convertible into 2,222,222 of the Issuer's common shares of beneficial interest</footnote>
        <footnote id="F4">Furthermore, Mr. Berkowitz and Fairholme Capital Management have disavowed management and supervision with respect to 570,995 shares of common stock held in the separate accounts of advisory clients, and, accordingly, Mr. Berkowitz and Fairholme Capital Management do not attribute such shares.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Bruce R. Berkowitz</signatureName>
        <signatureDate>2006-05-12</signatureDate>
    </ownerSignature>
</ownershipDocument>
