One of the very important barriers for proton exchange membrane fuel cells (PEMFCs) is the decrease in proton conductivity of membrane at elevated temperature and low relative humidity. In this study, inorganic-organic hybrid membranes have been developed in order to improve water retention and proton conductivity at elevated temperature. Using in situ self-assembly technique, the well-dispersed metal oxide nanoparticles (SiO2, ZrO2) with diameters of similar to 5 nm can be formed through sol-gel process in Nafion dispersion. It was found that the doped metal oxide nanoparticles did not affect the crystallinity and structure of Nafion (R) in the membrane significantly. Compared to Nafion (R) membrane, hybrid membranes show better water retention properties and higher proton conductivity at relatively low relative humidity. (C) 2009 Elsevier B.V. All rights reserved.