Preparation of phosphoric acid composite membranes by radiation induced grafting of 4-vinylpyridine (4-VP) onto electron beam irradiated poly(ethylene-co-tetrafluoroethylene) film followed by phosphoric acid doping was investigated. The effect of grafting parameters (monomer concentration, absorbed dose, reaction time, and temperature) on the degree of grafting (G%) in the membrane precursor and its relation with the amount of acid doped was studied. The proton conductivity of the obtained membranes was evaluated in correlation with G% and temperature using ac impedance. Fourier transform infrared, thermal gravimetric analysis, X-ray diffraction, and universal mechanical tester were used to investigate chemical composition, thermal resistance, structure, and mechanical properties of the membranes, respectively. The membranes of 34 and 49% recorded high proton conductivity in the magnitude of 10(-2) S cm(-1) without humidification. The membranes were also found to have reasonable mechanical integrity together with thermal stability up to 160 degrees C. The obtained membranes are suggested to be less-water dependent and have potential for testing in high temperature polymer electrolyte membrane fuel cell. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 549-557, 2013