An object of this invention is to provide an electrolytic membrane excellent in ion conductivity and oxidation resistance, and this invention is directed to an electrolytic membrane formed of a polymer comprising at least one recurring unit selected from the group consisting of a recurring unit of the following formula (A), and a recurring unit of the following formula (B), and having a reduced viscosity, measured in a methanesulfonic acid solution having a concentration of 0.5 g/100 ml at 25° C., of 0.05 to 200 dl/g, and a process for the production thereof.