Optimal distributions of Nation content and Pt loading across the entire thickness of cathode catalyst layers of polymer electrode membrane (PEM) fuel cells are obtained by maximizing the cell current density at a given potential. When optimization is performed with either the Nafion content or Pt loading as the single variable, it is found that the optimal distribution is a linearly increasing function from the gas diffusion layer side to the membrane side; when optimization is treated as a two-variable problem, i.e. comprising of both Nafion content distribution and Pt loading distribution, the optimal distribution of Nafion content is still a linearly increasing function but the optimal distribution of Pt loading is a convex increasing function. © 2004 Elsevier Ltd. All rights reserved.