Proton exchange membranes based on Nafion/poly(p-phenylene vinylene) (PPV) composites were prepared by the heat treatment of a Nafion/PPV precursor, and investigated regarding their applicability for direct methanol fuel cells (DMFCs). The power density of MEA using Nafion/PPV composites was increased with increasing the PPV precursor concentration of the precursor solutions and reached 34 mW/cm(2), which is much greater than that using bare Nation (similar to 26 mW/cm(2)). The improved MEA performance was primarily due to a significant decrease in the methanol permeability with only a minimal loss of the ionic conductivity through the formation of PPV grains inside of the ionic channels and on the Nation surface. The structure and properties of the Nafion/PPV composites were characterized by UV-vis spectroscopy, scanning electron microscopy, ion exchange capacity, water contact angle, and water uptake. (c) 2007 Elsevier B.V. All rights reserved.