A new method based on hydrogen pump is presented to measure the electro-osmotic drag coefficient and proton conductivity in Nafion (R) 117 membrane under similar condition to operating PEMFC. For membranes in contact with liquid water on both sides, electro-osmotic drag coefficient and proton conductivity increase with increasing temperature over the range of 20-90 degrees C while keeping water content inside the membrane constant (lambda=22.5) and decrease with decreasing water content in the membrane while keeping temperature of system constant (T = 25 degrees C). On the basis of cluster-network model and transport mechanisms of proton and water in ionomeric membrane, the results are discussed. (C) 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.