A new method of the formation of composite polypyrrole films containing a highly dispersed three-dimensional array of platinum catalyst particles is presented. PtCl42- anions were trapped inside the polypyrrole matrix during the electropolymerization or pyrrole. In the next step followed by solution exchange, PtCl42- anions were reduced to Pt-o particles with an average size of 10 nm. Metallic particles were incorporated in electrically conducting polypyrrole films in order to achieve multielectron-transfer processes in a three-dimensional matrix. These films were characterized using the electrochemical quartz crystal microbalance technique. The use of this technique allowed us to evaluate the Pt-o loading inside the polymer film. The electropolymerization process was controlled by measuring frequency changes of piezoelectrodes. The presence of Pt-o particles in composite polypyrrole films and their uniform distribution were confirmed by energy-dispersive x-ray spectroscopy and x-ray diffraction. The size of the Pt-o particles was evaluated from transmission electron microscopy experiments. The electrocatalytic effect toward the methanol oxidation was observed. Larger surface area and higher catalytic activity were found for electrodes with dispersed Pt-o nanoparticles in the polymer matrix than electrodes with electrodeposited Pt-o on the surface of the conductive polymer.