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

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-04-06</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001295079</issuerCik>
        <issuerName>Shengtai Pharmaceutical, Inc.</issuerName>
        <issuerTradingSymbol>SGTI.OB</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001488093</rptOwnerCik>
            <rptOwnerName>Ye Hu</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>CHANGDA ROAD EAST DEVELOPMENT DISTRICT</rptOwnerStreet1>
            <rptOwnerStreet2>CHANGLE COUNTY</rptOwnerStreet2>
            <rptOwnerCity>SHANDONG</rptOwnerCity>
            <rptOwnerState>F4</rptOwnerState>
            <rptOwnerZipCode>262400</rptOwnerZipCode>
            <rptOwnerStateDescription>CHINA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Options to purchase Common Stock</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>2.6</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2010-04-06</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>300000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <value>2011-04-06</value>
                <footnoteId id="F1"/>
            </exerciseDate>
            <expirationDate>
                <value>2020-04-05</value>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>300000</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>300000</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">This option (the &quot;Option&quot;) was issued pursuant to the Company's 2007 Stock Incentive Plan and the Nonstatutory Stock Option Agreement dated April 6, 2010. The Opiton shall become exercisable during the term of Mr. Hu Ye's employment in 3 equal annual installments of 100,000 shares each, the first installment to be exercisable on the first anniversay of the date of Option, and each subsequent installment on each anniversary thereof.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/Hu Ye</signatureName>
        <signatureDate>2010-04-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
