A novel organic-inorganic mesoporous silica (L64 copolymer-templated mesoporous SiO2), functionalized with perfluoroalkylsulfonic acid groups analogous to that of Nation (R), was prepared. A condensation reaction between the surface silanol groups of the mesoporous silicas and 1,2,2-trifluoro-2-hydroxy-1-trifluoromethylethane sulfonic acid Beta-sultone was conducted. High proton-conducting Nafion (R)/functionalized mesoporous silica composite membranes were prepared via homogeneous dispersive mixing and the solvent casting method. In this investigation, the proton conductivity (sigma) of the composite membrane is increased from 0.10 to 0.12 (S cm(-1)) as the modified mesoporous silica content is increased from 0 to 3 wt%. The methanol permeability of the composite membrane declined as the sulfonic mesoporous silica content increased. The methanol permeability of the composite membrane that contained 3 wt% M-SiO2-SO3H was 4.5 x 10(-6) cm(2) S-1-30% lower than that of pristine Nation (R). Results of this study demonstrate a significant improvement in the performance of DMFCs. (C) 2007 Elsevier B.V. All rights reserved.