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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4/A</documentType>

    <periodOfReport>2019-10-29</periodOfReport>

    <dateOfOriginalSubmission>2019-10-30</dateOfOriginalSubmission>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000717954</issuerCik>
        <issuerName>UNIFIRST CORP</issuerName>
        <issuerTradingSymbol>UNF</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001260756</rptOwnerCik>
            <rptOwnerName>CROATTI CYNTHIA</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O UNIFIRST CORP</rptOwnerStreet1>
            <rptOwnerStreet2>68 JONSPIN ROAD</rptOwnerStreet2>
            <rptOwnerCity>WILMINGTON</rptOwnerCity>
            <rptOwnerState>MA</rptOwnerState>
            <rptOwnerZipCode>01887</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Executive VP and Treasurer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2019-10-29</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1174</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4057</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>68534</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F3"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By LLC</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Stock Appreciation Right</value>
                <footnoteId id="F4"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>201.24</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2019-10-29</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>1669</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <value>2029-10-29</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock ($0.10 par value)</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1669</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1669</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
        <derivativeHolding>
            <securityTitle>
                <value>Class B Common Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F5"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock ($0.10 par value)</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>146779</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>146779</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F6"/>
                    <footnoteId id="F7"/>
                    <footnoteId id="F8"/>
                    <footnoteId id="F9"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Trust</value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
        <derivativeHolding>
            <securityTitle>
                <value>Class B Common Stock</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <footnoteId id="F5"/>
            </conversionOrExercisePrice>
            <exerciseDate>
                <footnoteId id="F5"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F5"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock ($0.10 par value)</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>1688694</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>1688694</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                    <footnoteId id="F6"/>
                    <footnoteId id="F10"/>
                    <footnoteId id="F11"/>
                    <footnoteId id="F12"/>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By Partnership</value>
                </natureOfOwnership>
            </ownershipNature>
        </derivativeHolding>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents restricted stock units granted under the UniFirst Corporation Amended and Restated 2010 Stock Option and Incentive Plan (the &quot;2010 Plan&quot;). Such restricted stock units vest 60% on the third anniversary of the grant date, 20% on the fourth anniversary of the grant date and 20% on the fifth anniversary of the grant date.</footnote>
        <footnote id="F2">Consists of 1,332 restricted stock units that vest 100% on December 20, 2022, 1,551 restricted stock units that vest 100% on October 22, 2023 and 1,174 restricted stock units that vest 60% on October 29, 2022, an additional 20% on October 29, 2023 and the remaining 20% on October 29, 2024.</footnote>
        <footnote id="F3">Cynthia Croatti is the manager of Trilogy Investment Partners LLC, which as of the date of filing this report, directly owns the reported securities. Cynthia Croatti disclaims beneficial ownership of these reported securities, except to the extent of her pecuniary interest therein, if any, and this report shall not be deemed an admission that she is the beneficial owner of the securities for purposes of Section 16 or any other purpose.</footnote>
        <footnote id="F4">This stock appreciation right, which was granted under the 2010 Plan, becomes 60% vested and exercisable on the third anniversary of the grant date (10/29/2022), an additional 20% vested and exercisable on the fourth anniversary of the grant date (10/29/2023) and an additional 20% vested and exercisable on the fifth anniversary of the grant date (10/29/2024). This stock appreciation right must be settled in stock at the time of exercise.</footnote>
        <footnote id="F5">Each share of Class B Common Stock is convertible at any time by the holder into one share of Common Stock. Each share of Class B Common Stock automatically converts into one share of Common Stock upon transfer to a recipient that is not a permitted transferee or upon termination of the Class B Common Stock, in each case in accordance with the terms of the charter of UniFirst Corporation.</footnote>
        <footnote id="F6">Each of the aforementioned reporting persons disclaims beneficial ownership of these reported securities, except to the extent of his, her or its pecuniary interest therein, if any, and this report shall not be deemed an admission that such persons are the beneficial owners of these securities for purposes of Section 16 or any other purpose.</footnote>
        <footnote id="F7">Includes 4,374 shares owned directly by The Marie Croatti QTIP Trust. Cynthia Croatti is trustee of The Marie Croatti QTIP Trust. Cynthia Croatti disclaims beneficial ownership of these reported securities, except to the extent of her pecuniary interest therein, if any, and this report shall not be deemed an admission that she is the beneficial owner of these securities for purposes of Section 16 or any other purpose.</footnote>
        <footnote id="F8">Includes 94,405 shares owned by trusts of which Cynthia Croatti is a trustee but not a beneficiary. Cynthia Croatti disclaims beneficial ownership of these reported securities, except to the extent of her pecuniary interest therein, if any, and this report shall not be deemed an admission that she is the beneficial owner of the securities for purposes of Section 16 or any other purpose.</footnote>
        <footnote id="F9">Cynthia Croatti is a trustee of The Samuel E. Brown Gallo Trust - 1989 and The Nicholas C. Brown Gallo Trust - 1989, which as of the date of filing this report, each directly owns a portion of an aggregate of 48,000 shares of Class B Common Stock. Cynthia Croatti disclaims beneficial ownership of these reported securities, except to the extent of her pecuniary interest therein, if any, and this report shall not be deemed an admission that she is the beneficial owner of the securities for purposes of Section 16 or any other purpose.</footnote>
        <footnote id="F10">Includes 672,775 shares owned directly by The Queue Limited Partnership and 199 shares owned directly by Queue Management Associates, Inc. Queue Management Associates, Inc. is the general partner of The Queue Limited Partnership. The Ronald D. Croatti Trust 1993 (of which Carol Croatti and Matthew Croatti are the trustees and Carol Croatti is the beneficiary), Cynthia Croatti and Cecilia Levenstein are the sole shareholders of Queue Management Associates, Inc., and Carol Croatti, Cynthia Croatti and Cecelia Levenstein are the directors of Queue Management Associates, Inc.</footnote>
        <footnote id="F11">Cynthia Croatti and Cecelia Levenstein are trustees, co-trustees and in some cases beneficiaries, and in some cases their children are beneficiaries, of various trusts which hold limited partnership interests in The Queue Limited Partnership. Ronald D. Croatti's children are beneficiaries of certain trusts which hold limited partnership interests in The Queue Limited Partnership. Certain of the trusts which hold limited partnership interests in The Queue Limited Partnership also own certain shares directly.</footnote>
        <footnote id="F12">Includes 1,015,717 shares owned directly by The Red Cat Limited Partnership and 3 shares owned directly by Red Cat Management Associates, Inc. Red Cat Management Associates, Inc. is the general partner of The Red Cat Limited Partnership. The Ronald D. Croatti Trust - 1993 and Cynthia Croatti are the sole shareholders of Red Cat Management Associates, Inc. and Carol Croatti and Cynthia Croatti are the directors of Red Cat Management Associates, Inc. Cynthia Croatti and Cecelia Levenstein are trustees, co-trustees and in the case of Cynthia Croatti a beneficiary of certain trusts which hold limited partnership interests in The Red Cat Limited Partnership. Ronald D. Croatti's children are beneficiaries of a trust which holds a limited partnership interest in The Red Cat Limited Partnership. Certain of the trusts which hold limited partnership interests in The Red Cat Limited Partnership also own certain shares directly.</footnote>
    </footnotes>

    <remarks>On October 30, 2019, the reporting person filed a Form 4 to report the grant of certain restricted stock units and a stock appreciation right (the &quot;Form 4&quot;). The Form 4 inadvertently reported incorrect vesting terms with respect to the restricted stock units and the stock appreciation right and an incorrect number of shares of Common Stock subject to the stock appreciation right. This Form 4/A is being filed to correct the vesting terms of the restricted stock units and stock appreciation right and to report the correct number of shares of Common Stock subject to the stock appreciation right.</remarks>

    <ownerSignature>
        <signatureName>/s/ David Whitman, Attorney-in-Fact</signatureName>
        <signatureDate>2019-12-04</signatureDate>
    </ownerSignature>
</ownershipDocument>
