The vapor phase oxidation of methanol over cupric salt catalysts of 12-heteropoly acids was studied in a fixed bed flow reactor at atmospheric pressure. The catalysts prepared were characterized by thermal analysis. IR absorption, ammonia adsorption, H₂ reduction, and by pretreating with various gases. Both acidity and oxidation ability of catalysts were affected by polyatom and the content of Cu²⁺ cation. The conversion of methanol over the catalysts with Mo as polyatom was much lower than that over the catalysts with W as polyatom, but the selectivity of formaldehyde was much higher; methanol was mainly dehydrated to dimethylether by strong acidic sites over the catalysts with W as polyatom. Increasing the content of Cu²⁺ cation in Cu_xH_3-2xPMo catalysts, the conversion of methanol was decreased, but the selectivity of formaldehyde was increased.