Mordenite membrane was prepared on alpha-Al2O3 tube by in situ hydrothermal synthesis with tetraethylammoniurn bromide (TEABr) as template agent. By the application of aging process of the parent solution, the size of mordenite crystals could be remarkably reduced from 20-30 (without aging) to 4-5 mum. The small crystal mordenite membrane had higher performance of pure gas permeation than big crystal mordenite membrane. The ideal selectivity of H-2/N-2 was 9.80, much higher than 3.82 of big crystals mordenite membrane. The membrane displayed high water-permselective performance in pervaporation (PV) test toward water/organic liquid mixtures. The highest separation factors achieved toward water/methanol, water/ethanol, water/n-propanol and water/i-propanol were 2600 (X-W = 50%, T = 323 K), 5500 (X-W = 50%, T = 343 K), 6000 (X-W = 15%, T = 343 K) and 6800 (X-W = 50%, T = 343 K), respectively.