NOVELTY - A membrane-electrode-gas-diffusion layer assembly (22) consisting of cathode-side gas-diffusion layer (4), cathode catalyst layer (2), polyelectrolyte membrane (1), anode catalyst layer (3), and anode-side gas-diffusion layer (5) is obtained by carrying out cathode sealing and anode sealing. The thickness of cathode catalyst layer, cathode-side gas-diffusion layer, and cathode-side gasket is set such that the ratio of sum total thickness of catalyst layer and diffusion layer is 1.2 or more with respect to the thickness of gasket, during cathode sealing.    USE - Manufacture of membrane-electrode-gas-diffusion layer assembly for use in polyelectrolyte fuel cells (all claimed) used for power generation.    ADVANTAGE - The method provides membrane-electrode-gas-diffusion layer assemblies which form polyelectrolyte fuel cells having excellent durability and power-generation characteristics.    DETAILED DESCRIPTION - A membrane-electrode-gas-diffusion layer assembly consisting of a cathode-side gas-diffusion layer, a cathode catalyst layer, a hydrocarbon type polyelectrolyte membrane, an anode catalyst layer, and an anode-side gas-diffusion layer laminated sequentially, is obtained by carrying out cathode sealing process and anode sealing process. The cathode sealing process involves providing a cathode-side gasket (6) on the end surfaces (4a,2a) of cathode-side gas-diffusion layer and cathode catalyst layer. The anode sealing process involves providing an anode-side gasket (7) on the end surfaces (5a,3a) of anode-side gas-diffusion layer and anode catalyst layer. The thickness of cathode catalyst layer, cathode-side gas-diffusion layer, and cathode-side gasket is set such that the ratio of sum total thickness of cathode catalyst layer and cathode-side gas-diffusion layer is 1.2 or more with respect to the thickness of cathode-side gasket, during cathode sealing process. The cathode catalyst layer and/or anode catalyst layer contain a catalyst substance, a solvent, and a polyelectrolyte. An INDEPENDENT CLAIM is included for method for improving durability of membrane-electrode-gas-diffusion layer assembly.    DESCRIPTION OF DRAWING(S) - The drawing shows a sectional view of the laminate used for manufacturing membrane-electrode-gas-diffusion layer assembly.    Polyelectrolyte membrane (1)    Cathode catalyst layer (2)    End surfaces of cathode-side gas-diffusion layer and cathode catalyst layer (2a,4a)    Anode catalyst layer (3)    End surfaces of anode-side gas-diffusion layer and anode catalyst layer (3a,5a)    Cathode-side gas-diffusion layer (4)    Anode-side gas-diffusion layer (5)    Cathode-side gasket (6)    Anode-side gasket (7)    Membrane-electrode-gas-diffusion layer assembly (22)