This study developed a transparent fuel cell to investigate the water flooding behavior on the cathode channel and analyzed its effect on the cell stability. The transparent cell was fabricated with gold-coated brass plate for the gas channel field and current collected rib. The transparent fuel cell was operated in a steady mode of constant current with the variations of cathode gas flow rate to observe the water flooding behavior in a cathode channel flow. The results revealed that the water flooding increases as the cell operated at a low flow rate and/or low cell temperature. The results indicated that at a high cell voltage (e.g. 0.7 V, electrochemical reaction region), water flooding was observed at low stoichiometric flow rate. At a low cell voltage (e.g. 0.45-0.5 V, 70 A), the performance was dominated by mass transport region. Maximum cell performance was observed at the oxygen stoichiometric flow rate of 6 for the cell temperature of 50 degrees C and humidified gas of 70 degrees C. Further increase of stoichiometric flow rate could increase the mass transfer rate, but also result in the drying of the membrane if the stoichiometric flow rate is too high. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All fights reserved.