Polymer electrolyte membrane, membrane electrode assembly, and fuel cell

Provided are a polymer electrolyte membrane, which includes an ion conductive domain having high continuity and a non-ion conductive domain and has a high strength, and a membrane electrode assembly and a fuel cell each using the polymer electrolyte membrane. The polymer electrolyte membrane includes a block copolymer having an ion conductive block and a non-ion conductive block and has a micro-phase separation structure constituted of an ion conductive domain including the ion conductive block and a non-ion conductive domain including the non-ion conductive block.