The performance of a proton exchange membrane fuel cell (PEMFC) is seriously changed by the humidification capability available when equipped with a PTFE (R) membrane. Typically, the humidification of a fuel cell is carried out by means of an internal or external humidifier. A membrane humidifier is applied to the external humidification of residential power generation fuel cell due to its convenience and high performance. In this study, a static model is constructed to understand the physical phenomena of the membrane humidifier in terms of geometric parameters and operating parameters. The model utilizes the concept of planar type heat exchanger with mass transport through the membrane. The model is constructed with FORTRAN in a Simulink (R) environment for consistency with other components of the model we previously developed. The results show that the humidity of the wet gas and the channel length, the membrane thickness and wet gas inlet humidity are critical parameters affecting the performance of the humidifier. (C) 2010 Elsevier Ltd. All rights reserved.