The Pd/C and Pt/C anodes modified with SnO2 nanoparticles for the polymer electrolyte fuel cell (PEFC) were investigated using pure and 500 ppm CO-contaminated H-2 as fuel gas. Modification of the Pd/C anode with SnO2 nanoparticles enhanced the cell performance in pure H-2, while modification of the Pt/C anode a little lowered the performance. The effect of SnO2 addition on the performances of the cell with the Pd anode in CO-contaminated H-2 was examined. The cell voltage with the Pd/SnO2/C anode in 500 ppm CO-contaminated H-2 was 0.41 V at a current density of 0.2 A/cm(2), while that in pure H-2 was 0.59 V. The Pd/SnO2/C anode exhibited good tolerance to CO poisoning, since the anode adsorbed CO more weakly. Neither electrochemical oxidation of CO nor shift reaction contributed to the CO tolerance of the Pd/SnO2/C anode.