A polymer electrolyte membrane comprising: (a) a fluorinated polymer electrolyte having an ion exchange group, and (b) a basic polymer, wherein, optionally, at least a part of component (a) and at least a part of component (b) are chemically bonded to each other. A method for producing the above-mentioned polymer electrolyte membrane. A membrane/electrode assembly comprising the above-mentioned polymer electrolyte membrane which is securely sandwiched between an anode and a cathode. A polymer electrolyte fuel cell comprising the membrane/electrode assembly.