To provide a method of producing a proton conductor membrane for a fuel cell for giving high gas shutoff capability thereto and causing no lower output of the fuel cell and a method of producing the fuel cell for achieving a high output.

The method of producing the proton conductor membrane comprises using such a fluid dispersion that a proton conductor is dispersed in a solvent to form the membrane of a proton conductor layer and volatilizing the solvent in the proton conductor layer to produce the proton conductor membrane, wherein pressure reducing treatment is applied to the proton conductor layer in a pressure reduced atmosphere after volatilizing the solvent.