Nafion/TiO2 composite membranes were studied for the application in proton exchange membrane fuel cell (PEMFC) to be used with the humidified or dry reactant gases of H-2 and O-2. Composite membranes were prepared by carrying out in-situ sol-gel reaction of Ti (OC4H9)(4) in Nafion perfluorosulfonic acid films, such as Nafion 112, 1135 and 115. The influence of the concentration of Ti (OC4H9)(4) isopropyl alcohol solution on the Ti content in the membranes of different thicknesses was investigated. The X-ray diffraction (XRD) analysis demonstrated that TiO2 in the composite membranes had a structure of anatase with an average particle size of 4.0 nm. The energy dispersive spectra (EDS) analysis indicated a symmetrical distribution of the TiO2 particles in the modified membranes. The water retention ability and electrochemical performance of Nafion/TiO2 composite membranes were evaluated using a single PEMFC operated with humidified or dry gas reactants during a long period. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.