Radiation-induced simultaneous grafting of styrene onto polytetrafluoroethylene (PTFE) films and the subsequent sulfonation in the chlorosulfonic acid/dichloroethane were investigated. The effects of the main radiation grafting conditions, such as the type of solvents, irradiation dose, dose rate, the styrene concentrations, etc., on the degree of grafting (DOG) were studied. To elucidate the influence of both the grafting and sulfonation conditions on the properties of the PTFE-g-polystyrene-sulfonic acid (PSSA) membranes, the sulfonation conditions, including the sulfonation temperature and the concentration of the CISO3H with respect to the DOG, were systematically evaluated. The grafted and sulfonated membranes were characterized by FTIR-ATR spectra, ion-exchange capacity (IEC), water uptake, thickness measurement, etc. The as-prepared PTFE-g-PSSA membranes in this work showed a good combination of a high IEC (0.85-2.75 meq g(-1)), acceptable water uptake (8.86-56.9 wt %), low thickness, and volume expansion and/or contraction. (c) 2005 Wiley Periodicals, Inc.