Abstract: An electrode substrate for fuel cells with a three-layer separator and two porous single or double carbonaceous layers and processes for preparing the same. The separator includes a carbon plate and two flexible graphite sheets. The porous layer has a number of elongated holes for feeding reactant gases into a fuel cell. The elongated holes are provided near the center of the thickness in the porous single layer or in the interface between the porous double layer. The electrode substrate exhibits improved properties, such as mechanical strength, thermal and electric resistances and the like, as a fuel cell electrode substrate.