To fabricate silane-crosslinked oraganic/inorganic hybrid proton exchange membranes (PEMs), poly(styrene sulfonic acid-co-(trimethoxysilyl)propyl methacrylate (TMSPM))-grafted ethylene-alt-tetrafluoroethylene (ETFE) membranes (ETFE-g-PSSA/PTMSPM) were prepared by a simultaneous irradiation grafting of various compositions of binary monomers (styrene and TMSPM) onto ETFE film and followed by hydrolysis-condensation and sulfonation to provide crosslinked structures and proton conducting ability, respectively. The effects of the individual degree of grafting of each graft polymer component on the chemical, physical, and morphological properties of the prepared PEMs, were also investigated. The results indicate that the silane-crosslinked PEM prepared with the monomers composition (Styrene (St)/TMSPM=5/5, v/v) has not only a lower water uptake but also a high proton conductivity, compared to those of ETFE-g-PSSA with similar ion exchange capacities (IEC). The silane-crosslinked PEM with 35% of the degree of grafting for PTMSPM were also found to have an improved chemical stability.