NOVELTY - The method comprises mixing carbon material, a binder and a solvent to prepare a coating composition, screen-coating the coating composition onto a diffusion layer (1) at a thickness of 20-50 mu m, and firing the coated diffusion layer to form a first microporous layer (2) that embeds into the diffusion layer. The first microporous layer has a thickness of 10-30 mu m, and a second microporous layer (3) forms a boundary with the diffusion layer. The second microporous layer is present on the surface of the embedded first microporous layer.    USE - The method is useful for preparing an electrode substrate of a membrane-electrode assembly for a fuel cell, which is useful in variety of applications such as mobile power sources for automobiles, distributed power sources for houses and public buildings and small electric sources for electronic devices, where the fuel cell is a power generation system for producing electrical energy through the electrochemical redox reaction of an oxidant and a fuel such as hydrogen or a hydrocarbon-based material such as methanol, ethanol and natural gas.    ADVANTAGE - The method is capable of effectively preparing the electrode substrate with improved performance such as increased diffusion properties, increased properties of releasing moisture and enhanced electron conductivity thus deteriorating interface resistance effects.    DETAILED DESCRIPTION - The method comprises mixing carbon material, a binder and a solvent to prepare a coating composition, screen-coating the coating composition onto a diffusion layer (1) at a thickness of 20-50 mu m, and firing the coated diffusion layer to form a first microporous layer (2) that embeds into the diffusion layer. The first microporous layer has a thickness of 10-30 mu m, and a second microporous layer (3) forms a boundary with the diffusion layer. The second microporous layer is present on the surface of the embedded first microporous layer. The coating composition comprises a solid content of 20-40 wt.%. The diffusion layer consists of carbon paper, carbon cloth, carbon felt and/or metal cloth, and has a thickness of 200-280 mu m.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of an electrode substrate for a fuel cell.    Diffusion layer (1)    First microporous layer (2)    Second microporous layer (3)    Electrode substrate. (10)