The effects of the residual water in the PEM fuel cell after cold start on the performance, electrode electrochemical characteristics, and cell components were investigated by controlling the cold-start processes of three cells at -5 degrees C. Neither the cell performance loss nor the cell resistance increase with the start number was observed. There was no change in the electrochemical active surface area (ECA) and charge transfer resistance at low current density. The correlation between the amount of the residual water and the ohmic polarization and cell resistance showed mass-transport process slightly changed with the water amount in the cell. This trend correlated well with the charge transfer resistance at high current density. The change of mass-transport process came from the gas diffusion layer by the analysis of ECA. It was found that hydrogen crossover rate of the membrane at the three hydrated states did not change through eight start-ups at -5 degrees C. Based on the analysis of SEM and water-storage capacity, it was believed that less water was stored in the catalyst layer even though much water resided in the cell. (c) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.