Co3O4-CeO2 catalysts prepared by the co-precipitation method have been studied for the preferential oxidation of carbon monoxide in hydrogen. Effects of the cobalt contents and calcination temperature on Co3O4-CeO2 were investigated, and the Co3O4-CeO2 catalyst containing 80 wt.% Co3O4 calcined at 350 degrees C exhibited the highest activity and good selectivity. The influence of the components of the feeding gas (H-2, CO2 and H2O) on the preferential oxidation of carbon monoxide had also been tested. The tested results showed that the negative effect of H-2 was much weaker than that of H2O and CO2.