A platinum/carbon nanofiber (Pt/CNF) nanocomposite with a platinum loading of 15 wt% is prepared by a modified electrophoretic deposition (EPD) method, and the as-grown nanocomposite is used as the electrocatalyst for oxygen reduction reaction (ORR). For comparison, a Pt/CNF composite with 40 wt% platinum loading is prepared by chemical reduction. High resolution transmission electron microscope (HRTEM) images show that the size of platinum nanoparticles formed by EPD is about 1 nm, much smaller than those by chemical reduction (about 3-5 nm). Cyclic voltammetric analysis in a nitrogen saturated electrolyte shows that the electrochemical surface area of electrocatalyst by EPD is larger than that by chemical reduction. Moreover, although the electrocatalyst prepared by chemical reduction has a higher electrochemical capacity, it is less active than that prepared by EPD. Analysis of the electrode kinetics using Tafel plot suggests that the electrocatalyst prepared by EPD provides a strong ORR activity. Cyclic voltammetric measurements at different scan rates confirm that the ORR on the nanocomposites prepared by EPD is a diffusion-controlled process. This work demonstrates that the Pt/CNF composites synthesized by EPD are effective for ORR. (C) 2007 Elsevier B.V. All rights reserved.