The oxygenation constants of transition-metal complexes with benzoin Schiff baseswere measured and these complexes were first employed as models for mimicking monooxygenasein catalytic epoxidation of styrene. The highest conversion and selectivity were up to 39.6% and100% respectively at ambient temperature and pressure. The effects of structures of the bridgegroup R in the ligands on the dioxygen affinities and catalytic activities to epoxidize styrene werealso investigated.