Proton exchange membranes consisting of Nafion (R) and crystallized titania nanoparticles have been developed to improve water-retention and proton conductivity at elevated temperature and low relative humidity. The anatase-type titania nanoparticles were synthesized in situ in Nafion solution through sol gel process and the size of the formed titiania nanoparticles is in the range of 3-6 nm. The formed nanoparticles are well-dispersed in Nafion solution at the titania concentration of 5 wt %. The glass transition temperature of the formed Nafion-titania composite membrane is about 20 degrees C higher than that of plain Nafion membrane. At elevated temperature (above 100 degrees C), the Nafion-titania nanocomposite membrane shows higher water uptake ability and improved proton conductivity compared to pure Nafion membrane. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1186-1192, 2011