LC-MS,　HPLC　and　atomic　absorption　spectrometry　were　used　to　reveal　the　reason　why　γ-oryzanol　leading　to　the　increase　of　free　fatty　acid　values　of　edible　oils　while　titrated　by　alkali.　When　phenolphthalein　was　used　as　indicator　to　determine　the　free　fatty　acid　values　of　oils,　the　hydrogen　atom　in　the　phenolic　hydroxyl　group　of　γ-oryzanol　appeared　to　be　weak　acidic　and　was　replaced　by　a　potassium　atom,　thus　resulting　in　the　excessive　consumption　of　alkali.　On　average,　38.96%　of　γ-oryzanol　transformed　into　potassium　derivatives　and　was　determined　by　atomic　absorption　spectrometry.　The　true　acids　value　of　the　free　fatty　acid　of　oils　including　γ-oryzanol　should　be　calculated　by　the　acids　value　observed　subtract　the　acids　value　caused　by　γ-oryzanol,　the　specific　formula　was　presented.　©　2015,　Chinese　Institute　of　Food　Science　and　Technology.　All　right　reserved.