<?xml version="1.0" encoding="UTF-8"?>
<edgarSubmission xsi:schemaLocation="http://www.sec.gov/edgar/thirteenffiler eis_13F_Filer.xsd" xmlns="http://www.sec.gov/edgar/thirteenffiler" xmlns:ns1="http://www.sec.gov/edgar/common" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <headerData>
    <submissionType>13F-NT</submissionType>
    <filerInfo>
      <liveTestFlag>LIVE</liveTestFlag>
      <flags>
        <confirmingCopyFlag>false</confirmingCopyFlag>
        <returnCopyFlag>true</returnCopyFlag>
        <overrideInternetFlag>false</overrideInternetFlag>
      </flags>
      <filer>
        <credentials>
          <cik>0000316369</cik>
          <ccc>XXXXXXXX</ccc>
        </credentials>
      </filer>
      <periodOfReport>06-30-2016</periodOfReport>
    </filerInfo>
  </headerData>
  <formData>
    <coverPage>
      <reportCalendarOrQuarter>06-30-2016</reportCalendarOrQuarter>
      <filingManager>
        <name>LIBERTY MUTUAL INSURANCE CO</name>
        <address>
          <ns1:street1>175 BERKELEY STREET</ns1:street1>
          <ns1:city>Boston</ns1:city>
          <ns1:stateOrCountry>MA</ns1:stateOrCountry>
          <ns1:zipCode>02116</ns1:zipCode>
        </address>
      </filingManager>
      <reportType>13F NOTICE</reportType>
      <form13FFileNumber>028-00033</form13FFileNumber>
      <otherManagersInfo>
        <otherManager>
          <form13FFileNumber>028-14589</form13FFileNumber>
          <name>Liberty Mutual Group Asset Management Inc.</name>
        </otherManager>
      </otherManagersInfo>
      <provideInfoForInstruction5>N</provideInfoForInstruction5>
    </coverPage>
    <signatureBlock>
      <name>Scott D. Fitzhenry</name>
      <title>Chief Compliance Officer</title>
      <phone>617-357-9500</phone>
      <signature>/s/ Scott D. Fitzhenry</signature>
      <city>Boston</city>
      <stateOrCountry>MA</stateOrCountry>
      <signatureDate>08-11-2016</signatureDate>
    </signatureBlock>
  </formData>
</edgarSubmission>
