ET-g-PAAc membranes were obtained by radiation grafting of acrylic acid onto poly(tetrafluoroethylene-ethylene) copolymer films using a mutual technique. The ion selectivity of the grafted membranes was determined toward K+, Ag+, Hg2+, Co2+, and Cu2+ in a mixed aqueous solution. The ion-exchange capacity of the grafted membranes was measured by back titration and atomic absorption spectroscopy. The Hg2+ ion content of the membrane was more than that of either the K+ or Ag+ ions. The presence of metal ions in the membranes was studied by infrared and energy-dispersive spectroscopy measurements. Scanning electron microscopy of the grafted and metal-treated grafted membranes showed modification of the morphology of the surface due to the adsorption of K+ and Ag+ ions. No change was observed for the surface of the membrane that was treated with Hg2+ ions. The thermal stability of different membranes was improved more with Ag+ and Hg2+ ions than with K+ ions. It was found that the modified grafted membranes possessed good hydrophilicity, which may make them promising candidates for practical applications, such as for cation-exchange membranes in the recovery of metals from an aqueous solution.