The predominant factor in catalytic low-temperature NO oxidation under an oxidative condition over supported Pt, Pd and Rh catalysts was investigated and discussed using a thermodynamic calculation, XPS analysis, CO adsorption, and reaction evaluation. New insights were gained as follows; the resistance to metal oxide formation of these metals is important for NO oxidation activity under an excess oxygen condition. In the fresh catalysts, the oxidation status of Pt was affected by the electronegativity of the support cation, and the Pt supported on a more acidic support has a higher NO oxidation activity. After aging treatment, the oxidation status of Pt on each support was almost the same, and a large amount of surface metallic Pt favors Pt catalysts to have high activity. The analysis of the NO oxidation kinetics revealed that the affinity of Pt for NO molecules was improved with the aging treatment. It could be concluded that a suitable combination of Pt and the support facilitates high dispersion of the metallic Pt, even after the aging treatment, which is favorable for the NO oxidation in the presence of excess oxygen at low temperature.