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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2009-11-05</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001473597</issuerCik>
        <issuerName>STR Holdings, Inc.</issuerName>
        <issuerTradingSymbol>STRI</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001443957</rptOwnerCik>
            <rptOwnerName>Jilot Dennis L.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>10 WATER STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>ENFIELD</rptOwnerCity>
            <rptOwnerState>CT</rptOwnerState>
            <rptOwnerZipCode>06082</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chairman, Pres &amp; CEO</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
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            <securityTitle>
                <value>Common Stock of Specialized Technology Resources, Inc.</value>
            </securityTitle>
            <transactionDate>
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            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
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            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
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                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
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                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
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                </natureOfOwnership>
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        </nonDerivativeTransaction>
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                </transactionShares>
                <transactionPricePerShare>
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        <nonDerivativeTransaction>
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                <value>Class A Units of STR Holdings (New) LLC</value>
            </securityTitle>
            <transactionDate>
                <value>2009-11-05</value>
            </transactionDate>
            <transactionCoding>
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                <footnoteId id="F1"/>
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            <transactionTimeliness>
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                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
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                <transactionShares>
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                </transactionShares>
                <transactionPricePerShare>
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        <nonDerivativeTransaction>
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                <transactionPricePerShare>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
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                <transactionFormType>4</transactionFormType>
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                </transactionShares>
                <transactionPricePerShare>
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            <postTransactionAmounts>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Units of STR Holdings (New) LLC</value>
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            <transactionDate>
                <value>2009-11-05</value>
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            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1000000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
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                </transactionAcquiredDisposedCode>
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            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By The Dennis L. and Linda L. Jilot Family Trust</value>
                </natureOfOwnership>
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        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Units of STR Holdings (New) LLC</value>
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            <transactionDate>
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                <transactionPricePerShare>
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        <nonDerivativeTransaction>
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                <transactionPricePerShare>
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        <nonDerivativeTransaction>
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            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>209505</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>612317</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Pursuant to a reorganization prior to the initial public offering of the Issuer, the holders of common stock of Specialized Technology Resources, Inc. received a proportionate amount of units in STR Holdings (New) LLC.  STR Holdings (New) LLC was then converted from a limited liability company into a corporation where the units of STR Holdings (New) LLC were converted into shares of common stock of the Issuer.</footnote>
        <footnote id="F2">31/60 of the options will vest on January 31, 2010 and the remaining options will vest ratably in equal 1/29 installments as of the last day of each of the successive 29 months thereafter.</footnote>
        <footnote id="F3">3/5 of the options will vest on January 31, 2010 and the remaining options will vest annually in equal installments over two years, commencing on December 31, 2010 subject to the Issuer's satisfaction of certain performance criteria. If the performance criteria is not met for the fiscal year ended December 31, 2010 but is met for the fiscal year ended December 31, 2011, then the yearly amounts for both fiscal years ended December 31, 2010 and 2011 will become vested.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Joseph C. Radziewicz, Attorney-in-fact</signatureName>
        <signatureDate>2009-11-10</signatureDate>
    </ownerSignature>
</ownershipDocument>
