Single-crystal Pt nanowires are directly grown oil carbon nanospheres via a simple chemical route, at room temperature in aqueous solution. The growth density and length of Pt nanowires oil the carbon support can be easily modulated. Of interest for PEM fuel cell application, such Pt nanowire/C composites show enhanced catalytic activity for the oxygen reduction reaction compared with a state-of-the-art Pt/C catalyst made of Pt nanoparticles.