A highly active Pt/carbon catalyst for polymer electrolyte membrane fuel cells and direct methanol fuel cells was prepared by using porous carbon that was synthesized by a colloidal-crystal templating method. The microstructure of the Pt/porous carbon composites was studied with N2 ad-/desorption isotherms, X-ray diffraction and transmission electron microscopy. In contrast to conventional carbon supports, the porous carbon exhibited an attractive microstructure as a catalyst support, i.e. a large surface area with mono-dispersed three-dimensionally interconnected mesopores (45nm). A large mesopore surface area prompted dispersion of Pt particles, which resulted in a large effective surface area of Pt with a high activity for the oxygen reduction reaction. The porous structure facilitated smooth mass transportation to give rise to high limiting currents.