Antioxidant activity of phytosterols, oryzanol, ferulic acid ester of sterols, corn fiber oil, and rice bran oil was investigated. Commercial soybean oil and distilled soybean oil FAME were used as substrates for both oxidative stability determination and viscosity analysis after the oil was oxidized. At low concentration, these materials did not improve the oxidative stability of the oil substrates, although the viscosity tended to be reduced slightly. The antipolymerization activity of steryl ferulate was higher at higher concentration than at lower concentration, and steryl ferulate was more effective than oryzanol. Rice bran oil showed very good antioxidant and antipolymerization activities.