The dynamic behavior of polymer electrolyte fuel cells was investigated experimentally at sudden load change conditions. The present study mainly focused on the variation of membrane hydration due to self-humidification. Steady-state results for various temperatures and humidities were used as the basic data for the analysis of dynamic behavior. Electrochemical impedance spectroscopy (EIS) showed that the ohmic resistance was reduced with the increase of humidity and current while the total polarization resistance including the mass transfer effect showed various trends according to cell temperature. The dynamic behavior of the cells was measured with time. The current increment just after an abrupt voltage reduction jumped to a certain level and then increased gradually, showing a logarithmic-shape curve. The stabilization time to steady-state was determined by using the curve-fitted lines representing the variation of the current increment at each operating condition. The stabilization time showed various trends according to cell temperature, humidity, and voltage range. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.