A method for producing a polymer electrolyte membrane of the present invention include the step of modifying a polymer electrolyte membrane which is salt-substituted with a polyvalent cation, by a modification treatment selected from a heat treatment, an active energy ray irradiation treatment and a discharge treatment, and preferably include the step of treating the modified polymer electrolyte with acid. This method allows a polymer electrolyte membrane capable of achieving methanol barrier properties and the proton conductivity at a high level.