Selective oxidation of carbon monoxide in high excess of H-2 was examined on noble metal catalysts (Pt, Ru, Pd, Co, and Pt-Ru) supported on mordenite. Pt-Ru/mordenite exhibited fairly high selectivity over a wide flow rate condition even at 150 degreesC. Thus, it seems to be a promising catalyst for polymer electrolyte fuel cells operated with reformed gas.