Four kinds of composite membranes were prepared by the solution-cast method with Nafion resin, poly(tetrafluoroethylene), and different types of SiO2. They are SiO2 sulfonated by 1,3-propane sultone (denoted as SiO2-1,3PS), SiO2 sulfonated by H2SO4 (denoted as SiO2-SO3H), and pure SiO2. The SiO2 content was controlled at 5% in the composite membranes. Combined with the results of the electrochemical impedance spectroscopy, water uptake, and fuel cell performance of different membranes, it suggested the organically modified SiO2 has a weak water uptake ability due to the organic molecule chain. (C) 2008 The Electrochemical Society.