The influence of post-treatment of as-synthesized mordenite membranes in the hydrochloric acid solution was investigated on the membrane pervaporation performance for the separation of a water/ethanol mixture. It was shown that the water/ethanol separation factor of as-synthesized mordenite membranes could be greatly improved upon post-treatment with hydrochloric acid under controlled conditions. The change in the pervaporation performance of mordenite membranes upon post-treatment was discussed. (C) 2007 Elsevier B.V. All rights reserved.