Carbon monoxide oxidation over the supported platinum catalysts was investigated. The catalyst of Pt/SnO2 exhibited superior catalytic activity despite the low surface area compared to Pt/gamma-Al2O3. It was confirmed by the temperature-programmed reduction analysis that the reduction of platinum species over Pt/SnO2 was initiated below room temperature. The platinum species reducible at lower temperature should be responsible for the high activity for the complete oxidation of carbon monoxide. Moreover, the influence of the reduction treatments on these supported platinum catalysts was studied. In the case of Pt/gamma-Al2O3, the catalytic activity was improved as the reduction temperature was elevated. This is because the adsorption sites of CO on platinum particles increased by the reduction at higher temperature, leading to the high catalytic activity. In contrast, the activity of Pt/SnO2 was enhanced even by the reduction at 25 degrees C and the catalyst reduced at 90 degrees C attained the highest activity. Correlations between the amount of adsorbed CO and the catalytic activity were observed in the Pt/gamma-Al2O3 system, which were not found in the reduced Pt/SnO2. These results suggest that the oxygen species of the SnO2 support activated by the reduction treatments contribute to carbon monoxide oxidation. The activity of the sample was significantly degraded by the reduction at 400 degrees C. This behavior was attributed to a decrease in reaction sites due to the formation of intermetallic compounds. (C) 2010 Elsevier B.V. All rights reserved.