A process comprising ultraviolet (UV)-induced photografting of styrene into polytetrafluoroethylene (PTFE) films and subsequent sulfonation has been developed for preparing proton-conducting membranes. The significance of this process is that the graft chains can penetrate throughout the PTFE base films; the resultant sulfonated electrolyte membrane with a low degree of grafting near 7% shows higher proton conductibility and better mechanical properties, similar to those of Nafion membrane. Furthermore, the performances of the UV-photografted electrolyte membranes are better as compared to those of the gamma-ray radiation grafted electrolyte membranes. (c) 2006 The Electrochemical Society.