A novel process comprising UV-induced photografting of styrene into poly(tetrafluoroethylene-co-ethylene) (ETFE) films in vapor and liquid phases, followed by electron beam-induced crosslinking to the ETFE-graft-polystyrene films, and finally sulfonation of the multiple-crosslinked films has been developed for preparing polymer electrolyte fuel cell membranes. The significance of this process is that the photografted polystyrene chains can completely penetrate into the base ETFE film; the resultant sulfonated electrolyte membranes show proton conductibility available for fuel cell applications. On one hand, the proton conductivity of the liquid-phase photografted electrolyte membranes is higher than the vapor-phase one, and is anisotropic in the surface and thickness directions. On the other hand, radiation-induced crosslinking greatly improves the chemical stability of the resultant fuel cell membranes, and maintains the surface concentration of sulfonic acid groups at its higher level, which are very important for the performance of the relevant membrane electrode assembly. (c) 2006 Elsevier B.V. All rights reserved.