Mordenite membranes have been prepared on the outer surface of a porous a-alumina tube by seed-assisted crystallization. The kind of silica source was found to have significant influence on the microstructure of the membrane grown on the seeded support. Highly water-selective mordenite membranes were prepared with crystallization time as short as 2-4 h at 180 degreesC. The dehydration of acetic acid by pervaporation was investigated using these thin membranes as functions of temperature and feed concentration. The separation mechanism is discussed. (C) 2003 Published by Elsevier Science B.V.