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

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2015-06-15</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0000100493</issuerCik>
        <issuerName>TYSON FOODS INC</issuerName>
        <issuerTradingSymbol>TSN</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001553018</rptOwnerCik>
            <rptOwnerName>Callahan Andrew P</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>400 S. JEFFERSON STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CHICAGO</rptOwnerCity>
            <rptOwnerState>IL</rptOwnerState>
            <rptOwnerZipCode>60607</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Pres Retail Packaged Brands</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-06-15</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>J</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>58</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>7748</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Class A Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2015-07-02</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>46587</value>
                    <footnoteId id="F3"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>54335</value>
                    <footnoteId id="F4"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares of the Issuer's Class A Common Stock received by the Reporting Person pursuant to the Issuer's dividend reinvestment plan since the last Statement of Changes in Beneficial Ownership was filed by the Reporting Person.  Such acquisitions are exempt from Section 16 concurrent reporting requirements pursuant to Rule 16a-11.</footnote>
        <footnote id="F2">Represents shares of Class A Common Stock which vest on the fourth business day following the filing the Issuer's Annual Report on Form 10-K for its 2017 fiscal year if the performance metric described in the applicable Stock Incentive Agreement is achieved.</footnote>
        <footnote id="F3">Award of Class A Common Stock which vests on July 1, 2018 if the performance metric described in the applicable Stock Incentive Agreement (the Incentive Agreement) is achieved and the Reporting Person is employed by the Issuer on the vesting date. The performance metric is achievement of a two year (fiscal 2016-2017) cumulative EBIT target as set forth in the Incentive Agreement.  If the performance metric is not achieved, the award expires.</footnote>
        <footnote id="F4">Includes 7,748 shares of Class A Common Stock which vest on the fourth business day following the filing the Issuer's Annual Report on Form 10-K for its 2017 fiscal year if the performance metric described in the applicable Stock Incentive Agreement is achieved.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ R. Read Hudson by Power of Attorney for Andrew P. Callahan</signatureName>
        <signatureDate>2015-07-07</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2015-06-15
0
0000100493
TYSON FOODS INC
TSN
0001553018
Callahan Andrew P
400 S. JEFFERSON STREET
CHICAGO
IL
60607
0
1
0
0
Pres Retail Packaged Brands
Class A Common Stock
2015-06-15
4
J
0
58
0
A
7748
D
Class A Common Stock
2015-07-02
4
A
0
46587
0
A
54335
D
Represents shares of the Issuer's Class A Common Stock received by the Reporting Person pursuant to the Issuer's dividend reinvestment plan since the last Statement of Changes in Beneficial Ownership was filed by the Reporting Person.  Such acquisitions are exempt from Section 16 concurrent reporting requirements pursuant to Rule 16a-11.
Represents shares of Class A Common Stock which vest on the fourth business day following the filing the Issuer's Annual Report on Form 10-K for its 2017 fiscal year if the performance metric described in the applicable Stock Incentive Agreement is achieved.
Award of Class A Common Stock which vests on July 1, 2018 if the performance metric described in the applicable Stock Incentive Agreement (the Incentive Agreement) is achieved and the Reporting Person is employed by the Issuer on the vesting date. The performance metric is achievement of a two year (fiscal 2016-2017) cumulative EBIT target as set forth in the Incentive Agreement.  If the performance metric is not achieved, the award expires.
Includes 7,748 shares of Class A Common Stock which vest on the fourth business day following the filing the Issuer's Annual Report on Form 10-K for its 2017 fiscal year if the performance metric described in the applicable Stock Incentive Agreement is achieved.
/s/ R. Read Hudson by Power of Attorney for Andrew P. Callahan
2015-07-07