Nanocomposite membranes based on the poly(vinyl alcohol) (PVA)/poly(sulfonic acid)grafted silica nanoparticles (PSA-g-SN) were prepared via solvent casting of PVA cross linked by glutardialdehyde in the presence of various amounts (0-20 wt%) of silica nanoparticles (SN), poly(styrene sulfonic acid)- (PSSA-g-SN) and poly (2-acrylamido-2-methyl-1-propane sulfonic acid)-grafted silica nanoparticles (PAMPS-g-SN) as hydrophilic inorganic modifiers. PSA-g-SN nanoparticles were synthesized by surface-initiated redox grafting of SSA and AMPS monomers from the surface of the aminopropylated silica nanoparticles. Membranes were then characterized by FTIR, impedance spectroscopy, thermogravimetric analysis (TGA), water uptake, tensile strength test and SEM. The best proton conductivity was observed for membranes containing S wt% of nanoparticles. Among three nanoparticles used, the highest proton conductivity (10.4 mS/cm) was observed for PVA membrane prepared in the presence of 5 wt% PAMPS-g-SN nanoparticles. Results showed that grafting of sulfonated monomer onto the silica nanoparticles enhances various properties, for example proton conductivity, of the polymer electrolyte membranes (PEMs). Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.