Zeolite T membranes were prepared by hydrothermal synthesis on porous mullite tubes seeded with zeolite T crystals, using milk-like aluminosilicate gel prepared from precipitated silica as a silica source with a molar composition Of SiO2:Al2O3:Na2O:K2O:H2O = 1:0.05:0.26: 0.09:14. After 30 h of the synthesis at 373 K, a zeolite crystal layer of about 20 mum in thickness was formed on the outer surface of the tube, which was composed of two layers, namely the top surface layer and the intermediate layer under the top surface layer. FE-SEM observation indicated the presence of well-intergrown zeolite T crystals packed densely in the intermediate layer, which appeared as an active layer for separation rather than the top surface layer. With increasing the kinetic diameter of gas from CO2 to C3H8, the gas permeance decreased by more than three orders in magnitude, indicating a very little amount of defects for the membrane. The membranes displayed high performance of pervaporation (PV) for water/organic liquid mixtures. The excellent PV performance was attributed to the combined effects of the preferential adsorption of water and the molecular sieving. The zeolite T membranes were stable in acetic acid solutions, but not in hydrochloric acid solution because of the dealumination. The zeolite T membranes also showed excellent performance of PV for water/acetic acid mixtures. (C) 2004 Elsevier B.V. All rights reserved.