Graphite nanofibers (GNFs)–supported platinum (Pt) catalysts had been prepared by an electrochemical deposition by controlling an applied potential to a potential of Pt reduction. Pt nanoparticles were successfully deposited by using potential sweep methods. The catalyst prepared by 18 sweep times showed the lowest resistance and the highest electroactivity. These electrochemical properties were dependent on the size, loading level, and morphology of catalysts. The influences of electrochemical condition on the sizes and loading level of catalysts were also investigated.