The mobility of water droplets and water films inside a straight micro-channel of a proton exchange membrane fuel cell was simulated to study the effects of the hydrophilic/hydrophobic properties on water behavior. The volume-of-fluid model in the FLUENT package was used to keep track of the deformation of the liquid-gas interface. The results show that the water moved faster on a hydrophobic surface. But a hydrophobic channel side-wall was a disadvantage for the gas diffusion when the MEA had a hydrophilic surface. A hydrophilic channel side-wall with a hydrophobic MEA surface could avoid water accumulation on the MEA surface. The water and gas distribution under this condition was advantageous for water discharge and gas diffusion. (c) 2006 Elsevier B.V. All rights reserved.