Abstract: Bi-Si mesoporous molecular zeolites(Bi-Si) was synthesized by the hydrothermal method with ethyl silicate （TEOS）as silica source, Bi(NO₃)₃·5H₂O as Bi source, and cetyltrimethylammonium bromide（CTAB）as template. Bi-Si catalyst had high ordering structures and high reaction activity in oxidation of styrene with hydrogen peroxide to benzaldehyde. The effects of solvents, reaction time, reaction temperature, oxidant concentration and Bi-Si concentration on the oxidation of styrene to benzaldehyde were studied systematically. It was found that in the following reaction conditions: catalyst 0.075 g, styrene 1.5 ml, methanol 25 ml，H₂O₂(30%) 4.5 ml，T=80 ℃，t=2 h，the conversion of styrene was 43.1%, the selectivity to benzaldehyde was 73.5%,the yield of benzaldehyde reached 31.7%.The possible reaction mechanism could be that one styrene molecule reacted with two H₂O₂ molecules on two joined catalytically active sites.