<?xml version="1.0"?>
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    <periodOfReport>2017-09-19</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001019048</rptOwnerCik>
            <rptOwnerName>LEATHERBY DENNIS</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>2200 W DON TYSON PARKWAY</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>SPRINGDALE</rptOwnerCity>
            <rptOwnerState>AR</rptOwnerState>
            <rptOwnerZipCode>72762</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Chief Financial Officer</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
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                <value>Class A Common Stock</value>
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            <securityTitle>
                <value>Class A Common Stock</value>
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                <natureOfOwnership>
                    <value>Employee Stock Purchase Plan</value>
                </natureOfOwnership>
            </ownershipNature>
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        <nonDerivativeTransaction>
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                <transactionCode>F</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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                <transactionPricePerShare>
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                </transactionPricePerShare>
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                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
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                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Performance Shares</value>
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            <transactionDate>
                <value>2017-11-17</value>
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                <transactionFormType>4</transactionFormType>
                <transactionCode>M</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
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            <transactionAmounts>
                <transactionShares>
                    <value>23662</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F4"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F4"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Common Stock</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>23662.0</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
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                <sharesOwnedFollowingTransaction>
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                </sharesOwnedFollowingTransaction>
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            <ownershipNature>
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                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </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">Includes 7,646.474 shares of Class A Common Stock which vested as described in footnote 6; 8,634.783 shares of Class A Common Stock which vest on the fourth business day following the filing of the Issuer's Annual Report on Form 10-K for its 2018 fiscal year if the performance metrics described in the applicable Stock Incentive Agreement are achieved; and 7,354.251 shares of Class A Common Stock which vest on November 17, 2019 if the performance metrics described in the applicable Stock Incentive Agreement are achieved.</footnote>
        <footnote id="F3">Represents shares of the Issuer's Class A Common Stock purchased for the Reporting Person's account under the Issuer's Employee Stock Purchase 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 16b-3.</footnote>
        <footnote id="F4">On November 21, 2014 the Reporting Person received a grant of 23,662 performance shares which vested (in whole or in part) or expired on November 17, 2017 subject to the achievement of performance criteria in the applicable Stock Incentive Agreement. The performance criteria were (a) a cumulative adjusted earnings before interest and taxes (EBIT) target of $8,704 million for the 2015-2017 fiscal years and (b) a favorable comparison of the Issuer's Class A common stock price relative to the stock prices of a predetermined peer group of publicly traded companies over the 2015-2017 fiscal years. The performance shares could vest at a level of 50%-200% and were previously reported as derivative securities at the 200% level. On November 17, 2017, 21,106.374 shares vested and are reported herein as acquired non-derivatives securities and 2,555.626 shares expired</footnote>
        <footnote id="F5">Pursuant to an election made by the Reporting Person, 10,311 shares were sold by the Reporting Person to the Issuer on November 17, 2017, to satisfy tax withholding obligations related to the vesting described in footnote 4.</footnote>
        <footnote id="F6">On November 17, 2017, 7,646.474 shares of restricted Class A Common Stock vested. These shares were previously reported as beneficially owned by the Reporting Person. Pursuant to an election made by the Reporting Person, 3,736 shares were sold by the Reporting Person to the Issuer on November 17, 2017, to satisfy tax withholding obligations.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ R. Read Hudson by Power of Attorney for Dennis Leatherby</signatureName>
        <signatureDate>2017-11-21</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2017-09-19
0
0000100493
TYSON FOODS INC
TSN
0001019048
LEATHERBY DENNIS
2200 W DON TYSON PARKWAY
SPRINGDALE
AR
72762
0
1
0
0
Chief Financial Officer
Class A Common Stock
2017-09-19
4
J
0
79.285
0
A
145352.27
D
Class A Common Stock
2017-11-16
4
J
0
344.0628
0
A
1770.2244
I
Employee Stock Purchase Plan
Class A Common Stock
2017-11-17
4
M
0
21106.374
0
A
166458.644
D
Class A Common Stock
2017-11-17
4
F
0
10311
0
D
156147.644
D
Class A Common Stock
2017-11-17
4
F
0
3736
0
D
152411.644
D
Performance Shares
2017-11-17
4
M
0
23662
0
D
Class A Common Stock
23662.0
0
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.
Includes 7,646.474 shares of Class A Common Stock which vested as described in footnote 6; 8,634.783 shares of Class A Common Stock which vest on the fourth business day following the filing of the Issuer's Annual Report on Form 10-K for its 2018 fiscal year if the performance metrics described in the applicable Stock Incentive Agreement are achieved; and 7,354.251 shares of Class A Common Stock which vest on November 17, 2019 if the performance metrics described in the applicable Stock Incentive Agreement are achieved.
Represents shares of the Issuer's Class A Common Stock purchased for the Reporting Person's account under the Issuer's Employee Stock Purchase 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 16b-3.
On November 21, 2014 the Reporting Person received a grant of 23,662 performance shares which vested (in whole or in part) or expired on November 17, 2017 subject to the achievement of performance criteria in the applicable Stock Incentive Agreement. The performance criteria were (a) a cumulative adjusted earnings before interest and taxes (EBIT) target of $8,704 million for the 2015-2017 fiscal years and (b) a favorable comparison of the Issuer's Class A common stock price relative to the stock prices of a predetermined peer group of publicly traded companies over the 2015-2017 fiscal years. The performance shares could vest at a level of 50%-200% and were previously reported as derivative securities at the 200% level. On November 17, 2017, 21,106.374 shares vested and are reported herein as acquired non-derivatives securities and 2,555.626 shares expired
Pursuant to an election made by the Reporting Person, 10,311 shares were sold by the Reporting Person to the Issuer on November 17, 2017, to satisfy tax withholding obligations related to the vesting described in footnote 4.
On November 17, 2017, 7,646.474 shares of restricted Class A Common Stock vested. These shares were previously reported as beneficially owned by the Reporting Person. Pursuant to an election made by the Reporting Person, 3,736 shares were sold by the Reporting Person to the Issuer on November 17, 2017, to satisfy tax withholding obligations.
/s/ R. Read Hudson by Power of Attorney for Dennis Leatherby
2017-11-21