Supported Cu catalysts were investigated for CO removal in a gas mixture after methanol steam reforming. Removal of CO in the post-reforming gas was effectively promoted by the addition of oxygen in the gas mixture. Not only water gas shift reaction (WGSR; CO + H2O --> CO2 + H-2) but also CO oxidation reaction (CO + 1/2O(2) --> CO2) was effective in reducing the CO concentration. Although, H-2 oxidation also proceeded by added oxygen, the concentration of CO significantly decreased without consuming a large amount of H-2 with an increase in oxygen concentration. The equilibrium concentration obtained from thermodynamic data indicates that the reaction is desirable at lower temperatures. Cu/Al2O3-ZnO demonstrated an excellent activity for catalytic removal of CO by oxygen-assisted WGSR. The activity was enhanced without increasing HZ conversion by employing longer contact time. These results indicate that the design of an active shift/oxidation catalyst operative at 100-150 degrees C is a possible method for removal of very small amounts of CO in the reformed fuel,