The aerobic oxidation of styrene to its epoxide catalysted by Salen-Mn(Ⅲ) complex was studied. Effects of amount of solvent, reaction temperature, reaction time, mole ratios of isobutyradehyde and catalyst to substrate on reaction were obtained. Conversion of styrene reached 98.3% , with a 85.9 % selectivity of epoxide, when reaction was run at 35 ℃ for 8 h with mole ratios of 2.5 and 0.35 % of isobutyradehyde and catalyst to the substrate, respectively. The catalyst was also applied to epoxidation of other olefins. Conversion decreased in the order of styrene, cyclohexene, 1-octene, 1-dodecene.