Manganese oxide octahedral molecular sieve (K-OMS-2) was prepared in the hydrothermal method. The K-OMS-2 was characterized with XRD, FT-IR, N2-adsorption and SEM, and was also employed as the catalyst for the vapor phase oxidation of toluene to benzaldehyde. It was shown that the K-OMS-2 prepared in the hydrothermal method had a morphology of nano-fiber with an average diameter of ca. 30 nm and length of above 1 μm. Compared with those prepared in the solid phase method and refluxing method, the K-OMS-2 prepared in the hydrothermal method exhibited a larger yield of benzaldehyde with obviously higher selectivity.