Composite membranes based on polytetrafluoroethylene (PTFE) and silicon dioxide (PTFE/SiO2 X HPO3) are fabricated to act as a fuel cell membrane for operation at temperatures from 120 to 200 degrees C. A porous PTFE membrane is used as the membrane supporting structure and SiO2 X HPO3 sol as the proton conductor. SEM and EDX show that the sol clusters are connected together and adhered to the PTFE polymer. This structure completely fills the pores of the PTFE and minimises the gas cross-over. The PTFE/SiO2 X HPO3 membrane has a high proton conductivity, up to 0.14?S?cm-1 at a relative humidity lower than 0.5%. The PTFE/SiO2 X HPO3 composite membrane gives the modest performance when it is tested in a hydrogen fuel cell although it is a potential material for the intermediate-temperature proton-conducting membrane fuel cell. Copyright (c) 2011 John Wiley & Sons, Ltd.