Synthesis and characterization of Nafion/TiO2 membranes for proton exchange membrane fuel cell (PEMFC) operating at high temperatures were investigated in this study. Nafion/TiO2 nanocomposite membranes have been prepared by in-situ sol-gel and casting methods. In the sol-gel method, preformed Nation membranes were soaked in tetrabutylortotitanate (TBT) and methanol solution. In order to compare synthesis methods, a Nafion/TiO2 composite membrane was fabricated with 3 wt.% of TiO2 particles by the solution casting method. The structures of membranes were investigated by Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), and Energy Dispersive X-Ray Analysis (EDXA). Also, water uptake and proton conductivity of modified membranes were measured. Furthermore, the membranes were tested in a real PEMFC. X-Ray spectra of the composite membranes indicate the presence of TiO2 in the modified membranes. In case of the same doping level, sol-gel method produces more uniform distribution of Ti particles in Nafion/TiO2 composite membrane than the ones produced by casting method. Water uptake of Nafion/TiO2 membrane with 3 wt.% of doping level was found to be 51% higher than that of the pure Nation membrane. EIS measurements showed that the conductivity of modified membranes decreases with increasing the amount of doped TiO2. Finally, the membrane electrode assembly (MEA) prepared from Nafion/Titania nanocomposite membrane shows the highest PEMFC performance in terms of voltage vs. current density (V-I) at high temperature (110 degrees C) which is the main goal of this study. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.