The effect of hydrothermal post-treatment in the hydrochloric acid solution was investigated on the pervaporation performance of mordenite membranes, with an emphasis on the influence of the acid concentration. The mordenite membrane with the water/ethanol separation factor of higher than 10,000 was successfully prepared via hydrothermal post-treatment in the hydrochloric acid solution of 0.2 mol dm(-3). The change in the pervaporation performance of mordenite membranes upon hydrothermal post-treatment was discussed. (c) 2007 Elsevier B.V. All rights reserved.