The effect of Ce promotion over 1wt% Pt/γ-Al_2O_3 catalysts on the CO conversion and CO_2 selectivity was investigated in preferential CO oxidation (PrOx) to reduce the CO concentration less than 10 ppm in excess H_2 stream for polymer electrolyte membrane fuel cell (PEMFC). Ce-promoted 1wt% Pt/γ-Al_2O_3 catalysts were prepared by incipient wetness impregnation method and the loading amount of Pt was fixed at 1wt%. The content of Ce promoter which has excellent oxygen storage and transfer capability due to the redox property was adjusted from 0 to 1.5wt%. Ce-promoted 1wt% Pt/γ-Al_2O_3 catalysts exhibit high CO conversion and CO_2 selectivity at low temperatures below 150℃ due to the improvement of reducibility of surface PtOx species compared with the 1wt% Pt/γ-Al_2O_3 catalyst without Ce addition. When Ce content was more than 1wt%, the catalytic activity was decreased at over 160℃ in PrOx because of competitive H_2 oxidation. As a result, 0.5wt% Ce is optimal content not only to achieve high catalytic activity and good stability at low temperatures below 150℃ in the presence of CO_2 and H_2O but also to minimize the H_2 oxidation at high temperatures.