${gamma}-Oryzanol$ is one of the chain breaking antioxidants. Both sterol (triterpene) and phenolic hydroxyl groups in the structure of ${gamma}-oryzanol$ may be responsible for its antioxidative function. We hypothesize that ${gamma}-oryzanol$ is more effective in preventing the autoxidation of polyunsaturated fatty acid (PUFA) than the synthetic phenolic compounds in an oil/water (O/W) emulsion system. The antioxidative effectiveness of different concentrations of ${gamma}-oryzanol$ and synthetic antioxidants was evaluated at different incubation times (0, 4, 8, 16, and 32 h) by measuring both the formation of hydroperoxides and the decomposition product of hydroperoxides (hexanal) in each emulsion system. Overall, the order of effectiveness of various antioxidants for inhibiting the formation of hydroperoxide in the O/W emulsion was: ${gamma}-oryzanol$> tert-butylhydroquinone (TBHQ)> butylated hydroxytoluene (BHT)> butylated hydroxyanisole (BHA). O/W emulsion with selective lower concentrations of ${gamma}-oryzanol$ showed better effectiveness than that with higher concentration of synthetic antioxidants. However, the ability of both ${gamma}-oryzanol$ and synthetic antioxidants to decompose hydroperoxide was similar. ${gamma}-Oryzanol$ was more effective antioxidant than the synthetic phenolic compounds in preventing the formation of hydroperoxide in the O/W emulsion system.