This study proposes a four-layer membrane electrode assembly (MEA) consisting of air-electrode, proton exchange membrane, Zn-electrode with KOH or NaCl aqueous electrolyte and a steel supporter, for use in Zn-air fuel cells. Montmorillonite clay was used to disperse carbon black (CB) and MnO2 catalyst to improve the performance of the air-electrode. The microstructures of the air-electrode and cell characteristics were investigated by field emission scanning electron microscopy (FE-SEM), optical microscopy (OM) and an electrochemical analyzer. The experimental results indicate that the four-layer MEA for Zn-air fuel cells reached a power density of 6 mW cm(-2) (at 10mA cm(-2)) without electrolyte leakage from the cells. The open circuit voltage (OCV) and current density were improved by adding clay to the air-electrode as clay can minimize CB aggregation. In the polarization test, the OCV value (1.40 V) reached approximately 90% of the standard potential (1.65 V) and remained steadily over 48 h. These experimental results demonstrate the four-layer MEA can replace conventional Zn-air fuel cells that utilize aqueous electrolyte. (C) 2007 Elsevier B.V. All rights reserved.