This paper describes the preparation and characterization of sulfonated polystyrene (SPS)/polytetrafluoroethylene (PTFE) composite membranes for direct methanol fuel cells (DMFCs). The SPS/PTFE composite membranes were prepared by adjusting the ratio of styrene/divinvibenzene (DVB) in reaction mixtures that were impregnated in porous PTFE substrate membranes. The soaked Substrates were then thermally polymerized and sulfonated with chlorosulfonic acid. SEM and ATR-FT-IR observations confirmed that the Porous PTFE substrates were filled Successfully with SPS. The water content, IEC values, the methanol permeability, and the ion conductivity increased with increasing ratio of styrene/DVB in the sulfonated membranes. The composite membranes showed comparable. or higher ion conductivity and lower methanol permeability than Nafion (R) 117 membrane, indicating that the composite membranes Could be an alternative membrane for DMFCs. (c) 2004 Elsevier B.V. All rights reserved.