Two different types of metals (Cu and Ni) and the effect of CeO2 addition to produce a CeO2-ZrO2 co-supporter were investigated through the water-gas shift (WGS) reaction. It was found that the WGS activity could be enhanced with CeO2 addition. At relatively high temperature, Ni-loaded catalysts exhibited higher CO conversion while Cu-loaded catalysts demonstrated better performance at low temperatures. The stability and yield of the CO2 and H-2 products of the Cu catalysts were higher than those of the Ni catalysts. These results may be caused by an irreversible adsorption of CO on Ni and the reverse WGS reaction occurring on the Ni catalysts. In situ diffuse-reflection infrared Fourier transform spectroscopy data suggests that the WGS mechanism likely proceeded via formate species.