The effect of TiO2 modification of the Pd/C anodes in polymer electrolyte fuel cells was investigated using pure H-2 and a CO/H-2 mixture. The modification of Pd/C anode catalyst with TiO2 increased the activity for electrochemical oxidation under pure H-2, and the TiO2-modified Pd/C anode catalyst showed high activity as well as the Pt/C catalyst. The cell voltages obtained at a current density of 0.2 A/cm(2) for Pt/C and TiO2-modified Pd/C were as high as 0.72 V. The addition of TiO2 increased the dispersion of metal particles, which resulted in an increase in the active surface area of the catalyst. In accordance with this result, CO pulse titration analysis showed that the metal dispersion of Pd/TiO2/C was higher than that of pure Pd/C catalyst. The effect of TiO2 addition on the performances of the cell with a Pd anode in a 500 ppm CO-contaminated H-2 fuel was also examined. These results show that the Pd/TiO2/C has a higher CO tolerance than Pt/C catalyst for maintaining high activity for electrochemical oxidation of H-2 in pure H-2.