Abstract: MoO₃-SnO₂ composite metal oxide catalyst was synthesized by one-step hydrothermal synthesis method without precipitant. The effect of MoO_x dispersion state on the catalytic performance of MoO₃-SnO₂ catalysts with different Mo/Sn molar ratios was investigated for dimethyl ether (DME) low-temperature oxidation to methyl formate (MF). MF selectivity reaches 77.6% with DME conversation of 22.0% over Mo₁Sn₂ at 150 ℃. The physiochemical properties of these catalysts were characterized by TEM, XRD, Raman, FT-IR, NH₃-TPD and H₂-TPR. The results showed that the addition of SnO₂ into MoO₃ affected the crystal structure of catalysts, forming MoO_x species with different degree of dispersion on the surface of SnO₂. The special architecture of MoO_x-SnO₂ plays a major role in modifying the acidity and the oxidizability of MoO₃-SnO₂ catalysts, leading to the obvious differences on catalytic activity.