A novel functional organoclay was prepared using POP-backboned quaternary ammonium salts that contained sulfonic acid (-SO3H) to improve the performance of Nafion (R) membranes used in direct methanol fuel cells. Modified layered silicate clays were cast with Nafion (R). The performance of the Nafion (R)/MMT-POPD400-PS composite membranes was evaluated in terms of methanol permeability, proton conductivity and cell performance. The methanol permeability of the composite membrane declined as the MMT-POPD400-PS content increased. The MMT was functionalized using organic sulfonic acid to enhance proton conductivity. The proton conductivity of the composite membrane exceeded that of pristine Nafion (R). These effects essentially improved the single-cell performance of DMFC. (C) 2007 Elsevier B.V. All rights reserved.