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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-03-22</periodOfReport>

    <notSubjectToSection16>1</notSubjectToSection16>

    <issuer>
        <issuerCik>0001088005</issuerCik>
        <issuerName>NextMart Inc.</issuerName>
        <issuerTradingSymbol>nxmr</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001471755</rptOwnerCik>
            <rptOwnerName>Liu Menghui</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>PINE VALLEY CENTER, 11TH FLOOR</rptOwnerStreet1>
            <rptOwnerStreet2>8 JIANGGUO MEN OUTER STREET</rptOwnerStreet2>
            <rptOwnerCity>BEIJING</rptOwnerCity>
            <rptOwnerState>J0</rptOwnerState>
            <rptOwnerZipCode>100022</rptOwnerZipCode>
            <rptOwnerStateDescription>GHANA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>1</isOther>
            <otherText>Former officer/director/10%</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>common stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <transactionDate>
                <value>2010-03-22</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>75000000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>By affiliate</value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">On March 22, 2010, an affiliate of the reporting person returned to the company 75,000,000 shares of common stock previously issued to the affiliate. In additon, 175,000,000 shares of common stock held for the benefit of the affiliate of the reporting person were also returned to the company.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ by Daniel H. Luciano as atty-in-fact for reporting person</signatureName>
        <signatureDate>2010-04-30</signatureDate>
    </ownerSignature>
</ownershipDocument>
