To provide a polymer electrolyte membrane having high proton conductivity without increasing the content of acid radicals in the polymer electrolyte membrane including the acid radical.

The polymer electrolyte membrane contains a block copolymer having a segment A including an acid radical and a segment B including essentially no acid radical, and has an ion exchange group equivalent weight of 150-5,000 g/mol. When glass transition temperature (C) of a homopolymer comprising the segment B including essentially no acid radical is denoted by X, storage elastic modulus of the polymer electrolyte membrane at X+10 (C) is 5.0108 or more, and the storage elastic modulus (Pa) of the polymer electrolyte membrane at X+10 (C) is 20% or more of the storage elastic modulus of the polymer electrolyte membrane at X-20 (C).