The effect of cathode gas diffusion media with microporous layers (MPLs) on direct methanol fuel cell (DMFC) performances is studied by combining electrochemical analysis and physicochemical investigation. The membrane electrode assemblies (MEAs) using MPL-modified cathode gas diffusion layers (GDLs, GDL-1) showed slightly better performances (117 mW cm(-2)) at 0.4 V and 70 degrees C than commercial GDL (SIGRACET (R) product version: GDL-35BC, SGL Co.) DMFC MEAs (110 MW cm(-2)). This might be due to high gas permeability, uniform pore distributions, and low water transport coefficient including methanol crossover. For GDL-1, the air permeability was 31.0 cm(3) cm(-2) s(-1), while the one for SGL 35BC GDLs was 21.7 cm(3) cm(-2) s(-1). Also, the GDL-1 in the pore-size distribution diagrams had distinct peaks due to more uniform distributions of macropores and micropores with smaller holes between aggregates of carbon particles compared to GDL-35 BC as confirmed by SEM images. Furthermore, the MEA using GDL-1 for the cathode had a lower water transfer coefficient compared to an MEA with a commercial 35 BC GDL. (c) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.