NOVELTY - Separator-diffusion layer assembly for a fuel cell assembly comprises a diffusion layer on a surface of a separator. The diffusion layer comprises an electroconductive film formed integrally with the separator and is formed with fluid paths extending through the diffusion layer in a direction of its thickness to be in flow communication with a recess of the separator.    USE - The separator-diffusion layer assembly is used for a fuel cell assembly (claimed).    ADVANTAGE - The diffusion layer has a reduced surface roughness, thus decreasing the contact resistance between the diffusion layer and its adjoining component part. It has an increased conductivity, and has a smaller thickness than the conventional diffusion layer, while maintaining a favorable diffusing function. The fuel cell assembly incorporating the separator-diffusion layer assembly eliminates the need for applying a large tightening pressure to the separators and the diffusion layers in the assembled state. This reduces the mechanical strength required to the component parts of the fuel cell assembly, thus decreasing its manufacturing cost. The influence of the stress that may be caused by expansion of the electrolyte layer in operation can be moderated, which eliminates the need for controlling the tightening pressure, and thus simplifies the operation.    DETAILED DESCRIPTION - Separator-diffusion layer assembly (130, 131) for a fuel cell assembly comprises a separator (115, 116) having a first surface formed with a recess (120) through which a fuel fluid or an oxidizing fluid flows and a second surface opposite to the first surface, and a diffusion layer (113, 114) on the first surface of the separator. The diffusion layer comprises an electroconductive film (133) formed integrally with the separator and is formed with fluid paths extending through the diffusion layer in a direction of its thickness to be in flow communication with the recess of the separator and thus diffuse the fluid in the recess on a side of a surface of the diffusion layer facing away from the first surface of the separator.    INDEPENDENT CLAIMS are also included for the following:    (a) a fuel cell assembly comprising an electrolyte layer, a pair of catalyst electrode layers interposing the electrolyte layer, a pair of separators each having a first surface facing the electrolyte layer and a second surface opposite the first, and a pair of diffusion layers; and    (b) a method for manufacturing a separator-diffusion layer assembly of a fuel cell assembly, which comprises: forming a diffusion layer on a surface of a substrate consisting of an inorganic material; and bringing an etchant into contact with the surface of the substrate through the fluid paths of the diffusion layer to form a recess in the surface of the substrate for allowing a fuel fluid or an oxidizing fluid to flow through the recess and thus making a separator.    DESCRIPTION OF DRAWING(S) - The figure is a schematic cross-sectional view for showing a fuel cell assembly.    Diffusion layer (113, 114)    Separator (115, 116)    Recess (120)    Separator-diffusion layer assembly (130, 131)    Electroconductive film (133)