A time dependence of three-dimensional simulation including water phase change and heat transfer of a PEMFC model has been studied. The overshoot behavior has been observed during a change in the electrical load during operation with fixed flow rates of hydrogen and air. The simulation of 25-cm2 active area with a serpentine flow path shows the interactions of the anode and cathode flow streams, the flow through the gas diffusion media, and the movement of water through the MEA by electroosmotic and back diffusion forces. The simulation used a commercial computational fluid dynamics (CFD) solver, STAR-CD with and add-on PEMFC module, es-pemfc. The operating conditions corresponded to 101kPa, 70°C cell temperature, anode and cathode dew points and stoichiometries of 78°C and 72°C and 1.2 and 2.0 at an initial operating voltage of 0.7V and current density of 0.57Acm−2.