A polymer electrolyte of high durability consistent with the present invention is characterized as including a first repeating unit represented by a general formula --{C(Z.sub.1)(Z.sub.2)--C(Z.sub.3)(Z.sub.4--SO.sub.3H)}-- (where Z.sub.1, Z.sub.2, Z.sub.3, and Z.sub.4 are respectively F or R.sub.f1, F or R.sub.f2, F or R.sub.f3, and nothing or R.sub.f4; and each of R.sub.f1, to R.sub.f4 is a perfluoroalkyl group in which the carbon number is from 1 to 10) in a polymer chain, and having an equivalent weight of 2500 g/eq or less.