The invention provides a proton conductive membrane excellent in heat resistance, which has sulfonic acid as ion exchange groups. The proton conductive membrane comprises a nitrogen-containing compound that can be mixed with water in arbitrary proportions and has a boiling point of not lower than 100. degree. C. and a proton conductive resin which has sulfonic acid ion-exchange groups, wherein the nitrogen-containing compound is contained in an amount of 0.5 to 10 parts by weight based on 100 parts by weight of the proton conductive resin.