In real catalyst system, it si difficult to establish a correlation between catalytic properties and the shape (crystal planes, corners and steps) of the active catalytic particles. In this paper we present a clear shape dependence of the catalytic properties of a Vulcan-supported fuel cell catalyst having 4 nm cubo-octahedral platinum(0) nanocrystallites with (111) and (100) surfaces stabilized by sodium polyacrylate. The electrode materials were characterized by CO-stripping cyclic voltammetry and transmission electron microscopy (TEM), showing that no agglomeration had occured among the nanoparticles on the catalyst surfaces.