A simple and fast empirical design model for a 5 kW proton exchange membrane (PEM) stack is presented in this paper. The performance analysis of the PEM stack operating on a membrane humidifying method is made through a series of experiments, including current-voltage-power characteristics, uniformity of cell unit voltages, gas pressure impact and air flux impact. Based on the above analysis, an empirical predicted model for the PEM stack has been developed by the combination of mechanistic and empirical modeling approaches to characterize and predict the voltage-current characteristics without examining in depth all physical/chemical phenomena. The good agreement between the predicted and experimental results covering a range of optimal operating conditions shows that the proposed model provides an accurate representation of the behavior for the PEM stack. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.