Pt-loaded carbon black for the catalyst of a PEM fuel cell was synthesized with different molar ratios of polyvinylpyrrolidone and H2PtCl6 solution to improve the dispersion of Pt nanoparticles on carbon black and decrease the size of Pt nanoparticles. From transmission electron microscopy results, Pt nanoparticles of a size of approximately 2 nm were highly dispersed when the polyvinylpyrrolidone concentration was 10mM. The electrochemical activity of the synthesized Pt/C catalysts was investigated by cyclic voltammetry, showing that the as-synthesized Pt-loaded carbon black catalyst had the best activity at a polyvinylpyrrolidone concentration of 10 mM.