Copper catalysts supported on alumina-based mixed oxides (Cu/Al2O3-MOx; M=Al, Ce, Co, Cr, Fe, Mg, Mn, Sn, Zn, and Zr) were investigated for CO removal in the methanol steam reformed gas. Cu/Al2O3-ZnO demonstrated excellent activity. The order of the activity for Cu/Al2O3-MOx with different M was Zn>Al>Cr>Mn>Mg. The highest catalytic activity is strongly related to the panicle size of Cu. Spinel type Cu-Al-Zn oxides, formed after the preparation, gave rise to fine Cu particles which deposited on the support by reduction so that high catalytic activity is led by small Cu particles. Excess amount of Cu (>30 wt%) leads to low dispersion and causes formation of large particles and deterioration of catalytic activity. Although it is difficult to remove the trace CO in the reformed gas through water-gas-shift reaction, addition of O-2 to the reformed gas is effective to enhance the CO removal through CO oxidation.