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

    <schemaVersion>X0202</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2008-01-23</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000726517</issuerCik>
        <issuerName>MERCHANTS BANCSHARES INC</issuerName>
        <issuerTradingSymbol>mbvt</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001220447</rptOwnerCik>
            <rptOwnerName>SKIFF ROBERT A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>275 KENNEDY DRIVE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SOUTH BURLINGTON</rptOwnerCity>
            <rptOwnerState>VT</rptOwnerState>
            <rptOwnerZipCode>05403</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2008-01-23</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>2450</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>23</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>5952.125</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F1"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Dr. Skiff's direct ownership of Merchants Bancshares, Inc. stock includes shares acquired through a dividend reinvestment plan, which provides for the regular reinvestment of dividends, broad-based participation and operates on substantially the same terms for all plan participants.</footnote>
    </footnotes>

    <remarks>This Form 4 is filed for the purpose of reporting distributions of Merchants Bancshares, Inc. stock received by Dr. Skiff from rabbi trusts under deferred compensation plans of Merchants Bancshares, Inc. and Merchants Bank on January 23, 2008.</remarks>

    <ownerSignature>
        <signatureName>Lisa A. Razo, P.O.A. for Robert A. Skiff</signatureName>
        <signatureDate>2008-01-24</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0202
4
2008-01-23
0
0000726517
MERCHANTS BANCSHARES INC
mbvt
0001220447
SKIFF ROBERT A
275 KENNEDY DRIVE
SOUTH BURLINGTON
VT
05403
1
0
0
0
Common Stock
2008-01-23
4
J
0
2450
23
A
5952.125
D
Dr. Skiff's direct ownership of Merchants Bancshares, Inc. stock includes shares acquired through a dividend reinvestment plan, which provides for the regular reinvestment of dividends, broad-based participation and operates on substantially the same terms for all plan participants.
This Form 4 is filed for the purpose of reporting distributions of Merchants Bancshares, Inc. stock received by Dr. Skiff from rabbi trusts under deferred compensation plans of Merchants Bancshares, Inc. and Merchants Bank on January 23, 2008.
Lisa A. Razo, P.O.A. for Robert A. Skiff
2008-01-24