A polymer electrolyte comprising an electrolyte salt, a non-aqueous solvent and a polymer which comprises repeating units of the formulas: --(R.sup.1 --O).sub.n --, and --[CH (R.sup.2)--CH.sub.2 --O].sub.m -- in which n.gtoreq.0 and m.gtoreq.0 provided that n+m.gtoreq.5, R.sup.1 is a C.sub.1 -C.sub.6 alkyl group, and R.sup.2 is a C.sub.1 -C.sub.6 alkyl group or a benzyl group, and a urea structure.