Water/unsymmetrical dimethylhydrazine (UDMH) mixtures were separated at ambient temperature and atmospheric pressure by pervaporation (PV) using NaA zeolite membranes. Effects of crystallization time and temperature on the membrane performance were studied. These membranes showed very high selectivity of water for water[UDMH mixtures. Separation factor as high as 52 000 was obtained for UDMH feed concentration of 5%. Total mass flux was also obtained up to 3.95 kg/m(2) h. The results confirm the superior performance of the zeolite membranes for dehydration of water/UDMH mixtures due to their uniform nanopores. (C) 2005 Elsevier B.V. All rights reserved.