Abstract: Provided are a process for producing a membrane/electrode assembly for a polymer electrolyte fuel cell and a process for producing a polymer electrolyte fuel cell, capable of achieving a high output voltage in a wide current density range. At least one of an anode and a cathode in a membrane/electrode assembly for a polymer electrolyte fuel cell is formed through a catalyst layer forming step of applying a first coating fluid containing a catalyst and an ion exchange resin, onto a substrate to form a catalyst layer; a gas diffusion layer forming step of applying a second coating fluid containing carbon fibers and an ion exchange resin, onto the catalyst layer to form a gas diffusion layer to serve as an outermost layer of the membrane/electrode assembly for the polymer electrolyte fuel cell; and a peeling step of peeling the substrate off from the catalyst layer.