The effect of the metal-gas diffusion layer (M-GDL) on the performance of a proton exchange membrane fuel cell (PEMFC) was investigated by numerically simulating selected parameters. Even though the ability of the M-GDL to outperform the conventional GDL is well known, it is necessary to optimise the design parameters of the M-DGL. This is to address its inefficient gas and electron transport due to the inherent heterogeneous structure. This paper presents the use of numerical simulation to quantify (a) the effect of the size of the pores and (b) width of the frame comprising the structure of a porous M-GDL in a PEMFC. A mechanical - electrical - electrochemical - fluid dynamics coupling model was utilised for this study involving an isothermal and single-phase simulation. The best cell performance was estimated as 0.63 Vat 1.5 A cm(-2) with the optimised M-GDL design, under the fully humidified condition with 30 mu m-thick Nafion. This constitutes a 9.4% improvement in cell performance.