Saline water electrolysis (SWE) is a representative electrochemical conversion process that produces hydrogen (H2), chlorine (Cl2), and sodium hydroxide (NaOH) at the same time, by applying electricity to saline water. SWE has been suffering from overpotentials much higher than its theoretical voltage of 2.2 V. The overpotentials come from high membrane resistance and/or interfacial resistance between its membrane and electrodes in zero-gap type. To solve this problem, water-soluble sulfonated polystyrene was chemically incorporated on both surface of chemically durable sulfonated poly (arylene ether sulfone) random copolymer via the simultaneous irradiation of electron-beam. The resulting membranes exhibited SWE performance superior to that of a commercially available Aciplex-F® membrane, owing to the synergistic effect of improved Na+ conductivity and reduced interfacial resistance.