Synthesis of monodisperse Pt nanocrystals with cubic and cuboctahedral shapes were successfully done by using a chemical reduction method. The catalytic performance of Pt nanoparticles toward methanol electrooxidation was measured. The results indicate that Pt cuboctahedra with external Pt{100} and Pt{111} crystallographic facets showed a higher catalytic activity for methanol electrooxidation than the commercial Pt/C catalyst.