Polymer Electrolyte Membrane Fuel Cell (PEMFC) system consists of many parts and the bipolar plate is one of the key components among them. Channels at the bipolar plate distribute air on the cathode side and hydrogen on the anode side, which are essential for the electric - chemical reaction to produce electricity. Bipolar plates may also be used as a path for the cooling water to control the temperature of the cell. There are several design parameters affecting the performance of the fuel cell system, and in this paper, the effects of geometric parameters are considered while others are fixed. It also discusses on how those design parameters affect the performance of the unit cell with the simple straight channel configuration. The parametric study has been conducted using commercial Computational Fluid Dynamics (CFD) techniques, and the results give designers the ideas on which combination between geometric design parameters would be optimal to get the best performance. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.