In order to develop a catalyst system for control of emissions from methanol-fueled vehicles, the activity in methanol and HCHO oxidation over supported metal oxides or gold catalysts was examined. Over supported metal oxide catalysts, large amounts of HCHO, CO and HCOOCH₃ was formed by partial oxidation, and the activities was very low. MoO₃/Al₂O₃ catalyst showed the highest activity. The activity of gold catalysts prepared by deposition method was much higher than that of supported metal oxide catalysts in spite of low loading of gold. Interestingly, methanol was completely oxidized to CO₂ and water. It was, as a reaction mechanism considered that the oxygen atom dissociated on the active site reacts with the methanol or the intermediates adsorbed on the support adjacent to active sites.