Cationic exchange membranes were prepared with 2,3-epithiopropyl methacrylate (ETMA)–methacryloyloxyethyl phosphoric acid (MP) copolymers. Transport of alkali metal and alkali earth metal ion against their concentration gradient through the UV-irradiated and nonirradiated membranes was investigated by using the system, where one side (L side) of the membrane in a diaphragm cell was acidic and the other (R side) alkaline or neutral, under various conditions. The ETMA–MP copolymer membranes transported rapidly alkali metal and alkali earth metal ion against their concentration gradient and the maximum transport fraction was more than 95%. The transport rate and transport fraction of metal ions was greatly affected by the composition of the copolymer membranes and H+ concentration in the L side. The transport selectivity between alkali metal ions was increased by using the E8P2 membrane UV-irradiated, but the degree of increase in the selectivity was not large. Ca2+ was transported more rapidly than Li+ against their concentration gradient.