The importance of membrane electrode assembly (MEA) conditioning for proton exchange membrane (PEM) fuel cells under various operating conditions, such as reactant flow and cell voltage-current combination, has been well recognized, but few studies have considered the impact of the cell hardware design. In this study, the impact of flow-field layout on the conditioning of MEAs has been experimentally investigated. It is shown that the MEAs conditioned with serpentine flow-field layouts on both the anode and cathode side have better performance than the MEAs conditioned with straight-parallel flow-field layouts, and that the peak power density can be increased from 0.83 W/cm(2) to 0.93 W/cm(2) (about 12% increase) for the MEAs tested under the same operating condition of using humidified hydrogen and air at atmospheric pressure. This performance improvement is mainly due to the under-rib convection of the reactant gases in serpentine flow-field layouts that provides more uniform conditioning of the entire MEAs, compared with the MEAs conditioned with straight-parallel flow-field layouts for which the portion of the MEAs under the rib is not well conditioned, due to the lack of the reactant flow there.