Sol-gel derived sulfonated diphenylclimethoxysilane (sDDS) with hydrophilic -SO3H functional groups were used as the additive to reduce the methanol permeability of Nation. The Nafion-sDDS (N-sDDS) nano-composite membranes were prepared by mixing Nafion-dimethyl formamide (DMF) solutions with sDDS sol and casting to membranes. Swelling weight (SW) test and SEM characterization show the physical properties of the composite membranes and FT-IR analysis reveals the incorporation of the sDDS monomer within the composite membranes. The composite membranes' methanol permeabilities are tested by gas chromatography according to the amount of the sulfonated silane. The cell performances of the N-sDDS membrane are evaluated and compared with the unsulfonated DDS composite membrane and Nafion (R) 117. It was found that, compared with the Nation (R) 117 membrane, the nano-composite membrane with the thickness of 125 mu m has a lower methanol permeability and better single cell performance than the unsulfonated DDS composite membrane. (c) 2005 Elsevier B.V. All rights reserved.