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Proc-Type: 2001,MIC-CLEAR
Originator-Name: webmaster@www.sec.gov
Originator-Key-Asymmetric:
 MFgwCgYEVQgBAQICAf8DSgAwRwJAW2sNKK9AVtBzYZmr6aGjlWyK3XmZv3dTINen
 TWSM7vrzLADbmYQaionwg5sDW3P6oaM5D3tdezXMm7z1T+B+twIDAQAB
MIC-Info: RSA-MD5,RSA,
 P5uLLyvxiRmVCpQU1hjTQvneUs7miVW8O7PRhpj7OHgXWFpjWBFHpPeJo/NSpxuE
 zIhucgDZ2GFxlMqL3+TJ7w==

<SEC-DOCUMENT>0001179110-10-014003.txt : 20100917
<SEC-HEADER>0001179110-10-014003.hdr.sgml : 20100917
<ACCEPTANCE-DATETIME>20100917215032
ACCESSION NUMBER:		0001179110-10-014003
CONFORMED SUBMISSION TYPE:	4
PUBLIC DOCUMENT COUNT:		1
CONFORMED PERIOD OF REPORT:	20100917
FILED AS OF DATE:		20100917
DATE AS OF CHANGE:		20100917

REPORTING-OWNER:	

	OWNER DATA:	
		COMPANY CONFORMED NAME:			BISHOP KENDALL R
		CENTRAL INDEX KEY:			0001195945

	FILING VALUES:
		FORM TYPE:		4
		SEC ACT:		1934 Act
		SEC FILE NUMBER:	001-34782
		FILM NUMBER:		101079423

ISSUER:		

	COMPANY DATA:	
		COMPANY CONFORMED NAME:			POWER ONE INC
		CENTRAL INDEX KEY:			0001042825
		STANDARD INDUSTRIAL CLASSIFICATION:	ELECTRONIC COMPONENTS, NEC [3679]
		IRS NUMBER:				770420182
		STATE OF INCORPORATION:			DE
		FISCAL YEAR END:			1231

	BUSINESS ADDRESS:	
		STREET 1:		740 CALLE PLANO
		CITY:			CAMARILLO
		STATE:			CA
		ZIP:			93012
		BUSINESS PHONE:		8059878741

	MAIL ADDRESS:	
		STREET 1:		740 CALLE PLANO
		CITY:			CAMARILLO
		STATE:			CA
		ZIP:			93012
</SEC-HEADER>
<DOCUMENT>
<TYPE>4
<SEQUENCE>1
<FILENAME>edgar.xml
<DESCRIPTION>FORM 4 -
<TEXT>
<XML>
<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0303</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2010-09-17</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <issuer>
        <issuerCik>0001042825</issuerCik>
        <issuerName>POWER ONE INC</issuerName>
        <issuerTradingSymbol>PWER</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001195945</rptOwnerCik>
            <rptOwnerName>BISHOP KENDALL R</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>740 CALLE PLANO</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>CAMARILLO</rptOwnerCity>
            <rptOwnerState>CA</rptOwnerState>
            <rptOwnerZipCode>93012</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2010-09-17</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>P</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>8000</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>8.24</value>
                    <footnoteId id="F1"/>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>150290</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This transaction was executed in multiple trades and the price above reflects the weighted average purchase price. The reporting person hereby undertakes to provide upon request to the SEC staff, the issuer or a security holder of the issuer full information regarding the number of shares and prices at which the transaction was effected.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>Tina D. McKnight, Attorney-in-Fact for Kendall R. Bishop</signatureName>
        <signatureDate>2010-09-17</signatureDate>
    </ownerSignature>
</ownershipDocument>
</XML>
</TEXT>
</DOCUMENT>
</SEC-DOCUMENT>
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