Ultrasonic bath cleaning technique was successfully applied for the pre-treatment of the gas diffusion electrode (GDE) before membrane-electrode assembly (MEA). The results show that ultrasonic bath pre-treatment significantly improves MEA performance in all current density regions, especially at the high current density region. This technique also reduces the time of the MEA conditioning, at least 30%. Electrochemical impedance spectroscopy (EIS) results demonstrate that pre-treatment of GDEs by ultrasonic bath technique leads to a decrease in the cell impedance especially in the ohmic resistance, which is very well due to the GDE cleaning process. The investigation of the GDE performance under different relative humidity (RH) of gases indicates that ultrasonic bath pre-treatment of the GDE is caused a delay in GDE flooding specially at high RH. This result demonstrates that removing non-bonded particles or creating new transfer passage by ultrasonic bath improves transfer of species within the GDE. GDE pre-treatment carried out in two ultrasonic bath solvents; water and an aqueous solution of isopropyl alcohol 10% (v/v). Results indicate that the aqueous solution of isopropyl alcohol 10% (v/v) can improve mass transfer of species within the electrode as well as water compared to the untreated GDE. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.