With a high-speed camera, water transport in the channels of a transparent proton exchange membrane fuel cell (PEMFC) was studied under different operating conditions. The results show that (a) Liquid water production under the banks is much bigger than that in the channels; liquid water close to channel walls can be easily changed into water film due to the hydrophilic capillary force of the walls and the drag force of the flow gas; liquid water on the surface of the gas diffusion layer (GDL) is near sphere drop due to its hydrophobic. (b) When gas velocity is less than 7 m/s, liquid water can not be moved swimmingly through the turns of the serpentine channel, and a part of liquid water will adhere to the walls; when gas velocity is more than 7 m/s, liquid water can be moved cleanlily through the turns. (c) Under the test conditions, when the temperature or the air stoichiometric ratio increases, liquid water production decreases, but cell performance is improved at first due to the increase of the electrochemical activity of the catalyst or the oxygen concentration, however the further increase of the temperature or air stoichiometric ratio will decrease the performance of the cell, because the membrane is dehydrated. These findings will help with the design and operation of the PEMFCs. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.