Abstract: The present invention discloses an improved gas diffusion layer for use in porous electrodes of polymer electrolyte fuel cells. The gas diffusion layer comprises a gas flow path having a bottom face facing an electrolyte membrane, and the properties of a carbon fiber that forms the bottom face of the gas flow path are different from the properties of a carbon fiber that forms the side wall of the gas flow path and/or the top face of the gas flow path. It is preferable that there is a difference in the graphitization degree, graphite orientation degree or fiber microstructure, and the hydrophilic group density of the carbon fiber forming the bottom face of the gas flow path is particularly small. Accordingly, it is possible to obtain a gas diffusion layer imparted with water retention property, without sacrificing the gas permeability.