To determine the net electro-osmotic drag coefficient of Nafion 115 and Hanwha membrane, we measured the fluxes of water discharged from anode and cathode at different current densities. Also, we investigated the contribution of water supply for membrane from anode and cathode. When the cathode was humidified, water supply for membrane at low current densities was achieved via the cathode, but the contribution of the anode became more important as current density gradually increased. The net electro-osmotic drag coefficient decreased sharply with current density, but it had a nearly constant value over 200 mA cm(-2). When the cathode was not humidified, at low current densities, most of water generated at cathode was supplied for membrane, but water supply from cathode at high current densities decreased proportionately, and the net electro-osmotic drag coefficient showed larger value.