The increase of the operation temperature in proton-exchange membrane fuel cell (PEMFC) above 100 degrees C is a great concern for the application of this type of cells in electric vehicles. Hybrid organic-inorganic membranes with nano-sized interfaces can combine the main properties to meet this objective. Methacrylate-silica covalent hybrid membranes have been synthesised by polymerization of 2-hydroxyethyl methacrylate and 3-methacryloxypropyl trimethoxysilane, and hydrolysis-polycondensation of alkoxide radicals. Tungstophosphoric acid hydrate was incorporated to endow the membranes with proton conductivity. The composition and synthesis conditions to promote organic polymerisation and sol-gel condensation avoiding phase separation have been optimised. The structural analysis shows homogeneous membranes without phase separation. The water retention properties provided by SiO2 and tungstophosphoric acid leads to high proton conductivity (maximum values around 3 x 10(-2) S cm(-1)) at 100-150 degrees C. A 0.5 M % of Tungstophosphoric acid (PWA) is enough to build well-connected paths for proton conduction. (c) 2005 Elsevier B.V. All rights reserved.