Layered silicate nanocomposite membranes to be used as electrolyte polymeric membranes in a direct methanol fuel cell were prepared through the mixing of poly(vinyl alcohol) (PVA) with various amounts (2, 4, and 5% w/w) of sodium montmorillonite layered silicate nano-clay. The proton conductivity of the polymer was induced by the reaction of the polymer with sulfosuccinic acid. Aft r that, a solution of the sulfonated PVA-layered silicate nanocomposite was cast into membranes. The proton conductivity and methanol permeability of the membranes were determined with a four-point probe technique and a gas chromatography technique, respectively. In addition, structures of the nanocomposite membranes were characterized with X-ray diffraction, differential scanning calorimetry, and Fourier transform infrared techniques. The mechanical properties of the nanocomposite membranes were also determined with a universal testing machine. From the results, it was found that the water uptake, proton conductivity, and methanol permeability of the membranes initially decreased after a 2% (w/w) concentration of the layered silicate was added. Above this nanoclay loading, the water uptake of the membranes increased again. The results were examined in the light of the interaction between the clay and sulfonated polymer, and the steric effect provided the exfoliation of the nanoclay. (c) 2008 Wiley Periodicals, Inc.