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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-09-27</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001139233</rptOwnerCik>
            <rptOwnerName>ASHNER MICHAEL L</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O WINTHROP FINANCIAL ASSOCIATES</rptOwnerStreet1>
            <rptOwnerStreet2>TWO JERICHO PLAZA WING A</rptOwnerStreet2>
            <rptOwnerCity>JERICHO</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>11753</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman and CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001271267</rptOwnerCik>
            <rptOwnerName>FUR INVESTORS LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>7 BULFINCH PLACE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 500</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02114</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001275105</rptOwnerCik>
            <rptOwnerName>FUR HOLDINGS LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>7 BULFINCH PLACE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 500</rptOwnerStreet2>
            <rptOwnerCity>BOSTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>02114</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001274894</rptOwnerCik>
            <rptOwnerName>WEM FUR INVESTORS LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>100 JERICHO QUADRANGLE</rptOwnerStreet1>
            <rptOwnerStreet2>STE 214</rptOwnerStreet2>
            <rptOwnerCity>JERICHO</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>11753</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Shares of Beneficial Interest</value>
            </securityTitle>
            <transactionDate>
                <value>2010-09-27</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>198400</value>
                    <footnoteId id="F2"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>12.25</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>3342950</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>see notes</value>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                    <footnoteId id="F5"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Shares acquired in Issuer's public offering.</footnote>
        <footnote id="F2">Shares were acquired by FUR Investors LLC (&quot;Investors&quot;), an entity wholly-owned by FUR Holdings LLC (&quot;Holdings&quot;), the managing member of which is WEM-FUR Investors LLC (&quot;WEM&quot;).  Michael Ashner is the managing member of WEM.  132,800 of the purchased shares are allocable to Michael Ashner.</footnote>
        <footnote id="F3">Shares are comprised of (i) 60,256 shares held directly by Michael L. Ashner and his wife, (ii) 3,242,032 shares held by Investors and (iii) 40,662 shares held by the Ashner Family Evergreen Foundation, a New York not for profit corporation (the &quot;Foundation&quot;), an entity in which the Reporting Person is a director.</footnote>
        <footnote id="F4">Each of the Reporting Persons disclaims beneficial ownership of the shares held by the Foundation.</footnote>
        <footnote id="F5">For purposes of Section 16 of the Act: (i) Investors beneficially owns 3,242,032 shares of Beneficial Interest, (ii) Holdings beneficially owns the number of shares of Beneficial Interest listed by Investors as held by Investors, (iii) WEM beneficially owns 1,498,730 shares of Beneficial Interest, and (iii) Mr. Ashner beneficially owns 1,232,874 shares of Beneficial Interest.  The shares held by Investors are subject to distribution to its members at any time upon request of such member. It is expected that substantially all of the 198,400 shares acquired will be distributed to the applicable members in early 2011.</footnote>
    </footnotes>

    <remarks>This statement is filed as a joint report pursuant to Rule 16a-3(j) promulgated under the Securities Exchange Act of 1934 (the &quot;Act&quot;) by the undersigned Reporting Person and by the entities listed on the attached Joint Filer Information Sheet who are deemed to constitute a &quot;group&quot; beneficially owning more than 10% of the Issuer's shares of beneficial interest, par value $1.00 per share under Section 13(d) of the Act.</remarks>

    <ownerSignature>
        <signatureName>Michael L. Ashner</signatureName>
        <signatureDate>2010-09-28</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>FUR Investors LLC</signatureName>
        <signatureDate>2010-09-28</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>FUR Holdings LLC</signatureName>
        <signatureDate>2010-09-28</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>WEM-FUR Investors LLC</signatureName>
        <signatureDate>2010-09-28</signatureDate>
    </ownerSignature>
</ownershipDocument>
