A novel supported catalyst has been prepared by the chemical deposition of Pt particles on a polypyrrole \ polystyrenesulphonate (PPY \ PSS) composite. The chemically prepared polymer particles were designed to provide a porous, proton and electron conducting catalyst support for use in fuel cells. Transmission electron microscopy, conductivity measurements, impedance spectroscopy, and cyclic voltammetry confirm that these properties have been achieved. The chemically prepared PPY \ PSS composite exhibits very high proton conductivities that are several orders of magnitude higher than for electrochemically prepared films. Currents of 0.1 A cm(-2) have been observed for oxygen reduction in proton exchange membrane (PEM) fuel cell type gas diffusion electrodes.