A membrane/electrode assembly comprising a pair of electrodes and an ion exchange membrane disposed therebetween wherein the ion exchange membrane contains a repetitive unit represented by the formula (I), and the minimum value of the internal resistance of the assembly at 80° C. and 120° C. is 100 mΩ·cm2 or less and 600 mΩ·cm2 or less, respectively:
in which, m and n is a positive integer, n/n+m is 0.001 to 1, Y is —S—, —S(O)—, —S(O)2—, —C(O)—, —P(O)(C6CH5)— or a combination thereof, Z is a single bond, —C(CH3)2—, —C(CF3)2—, —C(CF3)(C6H5)—, —C(O)—, —S(O)2— or —P(O)(C6H5)—, and A represents a sulfonate-containing moiety.