Poly (ethylene-co-tetrafluoroethylene) (ETFE) membranes were irradiated by electron beams and then acrylic acid (AA) and sodium styrene sulfonate (SSS) were grafted onto the membranes, in an attempt to prepare cation exchange membranes containing -COOH and -SO3Na groups. The grafting yield was found to be strongly dependent on the synthesis condition such as irradiation dose, co-monomer composition. Infrared spectroscopy of the grafted membrane confirmed the existence of sulfonate and carboxylic acid groups. The membrane resistance decreases with the increasing of grafting yield