High-quality zeolite silicalite-1 membranes of large area (78.5cm2) were prepared on porous tubular stainless steel supports with optimized synthesis solution composition by two-stage varying-temperature in situ synthesis. Compared with the synthesis at constant temperature (one-stage), the two-stage varying-temperature in situ synthesis generated a thin and dense membrane, since a large number of new nuclei could form at low temperature, while the crystallization temperature was rapidly changed to a high temperature after completion of the nucleation period, a thin and continuous membrane would quickly formed on the support by the nuclei regrowth. The membranes were characterized by X-ray diffraction, scanning electron microscopy and single-gas permeation. These results indicated that the membranes prepared by the two-stage varying-temperature in situ synthesis method exhibited high gas permeation performance and good reproducibility. The H2 permeance and H2/n-C4H10 selectivity of the membranes made by two-stage varying-temperature in situ synthesis method reached 12.25 x 10-7mol/m2sPa and 46.1, respectively. The yield of high-quality membranes with perm-selectivity of H2/n-C4H10 larger than 25 (almost 5 times as large as the Knudsen factor) as a quality criterion reached 70% of all preparations. By comparison of their permeability and reproducibility with those reported in the literature, it was revealed that the prepared membranes by two-stage varying-temperature in situ synthesis method were of good quality. Moreover, their thermal stability were tested in a gas mixture of ethylbenzene and hydrogen at high temperature, for an example, the membrane having the separation selectivity of hydrogen and ethylbenzene mixture as high as 190 was stable after 80h at 400C.Preparation of Silicalite-1 Membranes on Stainless Steel Supports by a Two-Stage Varying-Temperature in situ Synthesis. C.Kong, J.Lu, J.Yang, J.Wang: Journal of Membrane Science, 2006, 285[1-2], 258-64