Influence of pore structure of the cathode catalytic layer in a PEMFC in its performance has been studied. Membrane-electrode assemblies were prepared to have various kinds of porosities and pore structures using spray-drying method. From the I-V characteristics of catalytic layers, pore structure seems to be an important factor determining the cell performance. Addition of thermoplastic agent seems to indeed enhance the structural stability and performance of the catalytic layer. Pore forming agent is considered to assist the transport of oxygen through the catalytic layer. (C) 2002 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.