A polymer electrolyte fuel cell comprising a cell having a solid polymer film, separators disposed on both sides of the cell so as to interpose the cell therebetween, and diffusion layers disposed between the cell and the separators and each having a substrate comprising an electrically conductive porous material and a slurry layer disposed on the substrate, wherein at least a part of each diffusion layer is provided with a gas barrier for preventing the permeation of gas in a direction parallel to the major surface of the diffusion layer.