A new fuel-cell electrocatalyst based on highly porous carbonized polyacrylonitrile (PAN) microcellular foam with platinum particles was prepared recently in this laboratory. Its surface morphology one of the most important aspects of a practical electrocatalyst. has been examined in terms of fractal theory and methods. The fractal dimension of the platinum particles dispersed in porous carbonized PAN foam was determined by using chronometric and rotating-disk-electrode methods in oxygen-saturated solutions. A fractal dimension smaller than 2 was obtained, which was attributed to the partially active nature of the surface of this electrocatalytic material. This value of fractal dimension is also proposed to be considered as a reaction dimension. A reaction dimension smaller than 2 may indicate that not all of the platinum particle surface is accessible to the incoming oxygen molecules.