Sulfonated-silica/Nafion (R) composite membranes were prepared in a sol-gel reaction of (3-Mercaptopropyl)trimethoxysilane (SH-silane) followed by solution casting, and then oxidated using 10wt% H2O2 solution. The chemical and physical properties of the composite membranes were characterized by using FT-IR, XPS, Si-29 NMR and SEM analyses. Experimental results indicated that the optimum oxidation condition was 60 degrees C for 1 h. The performance of the silica-SO3H/Naflon (R) composite membranes was evaluated in terms of methanol permeability, proton conductivity and cell performance. The silica-SO3H/Nafion (R) composite membranes have a higher selectivity (C/P ratio= 26,653) than that of pristine Nafion (R) (22,795), perhaps because of their higher proton conductivity and lower methanol permeability. The composite membrane with 0.6 wt% silica-SO3H/Nafion (R) performed better than pristine Nafion (R). The current densities were measured as 62.5 and 70mA cm(-)(2) at a potential of 0.2 V with a composite membrane that contained 0 and 0.6 wt% silica-SO3H, respectively. The cell performance of the DMFC was improved by introducing silica-SO3H. The composite membrane with 0.6 wt% of silica-SO3H yielded the maximum power density of 15.18MW cm(-2). The composite membranes are suitable for DMFC applications with high selectivity. (C) 2007 Published by Elsevier B.V.