Pt-Pd nanoparticles supported on carbon black were prepared and characterized as electrocatalysts for methanol oxidation and oxygen reduction in an acidic solution. The Pt and Pd nanoparticles were impregnated spontaneously on the carbon black through a simple reducing process. X-ray diffraction, transmission electron microscopy, and electrochemical measurement were carried out to characterize the crystal structure, particle size, and catalytic activities of the Pt-Pd catalysts. The results showed that the Pt-Pd catalysts had higher catalytic activities for methanol oxidation reaction than pure Pt catalysts. The catalytic activity of the Pt-Pd catalysts for oxygen reduction reactions in the presence of methanol was higher than that of pure Pt and Pd. These results indicate that the Pt-Pd catalysts are suitable as electrocatalysts of both the anode and the cathode in direct methanol fuel cells.