A thin and compact mesoporous MCM-48 membrane had been successfully synthesized on vacuum-coated alpha-Al2O3 support with pore size of 1 mu m. The pretreated supports and the membranes were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and single gas permeation test. The pretreated supports were gas permeable for N-2 and the as-synthesis membrane was gas tight, indicating that the defects left in the vacuum step disappeared in the multi-hydrothermal synthesis process. The XRD pattern of the membrane was represented to the typical cubic laid space group. And the SEM images showed that the membrane was continuous and 4-mu m thick. Additionally, the separation factor of the calcined membrane for H-2/N-2 was up to 3.33 and the Knudsen contribution to the total flux for N-2 permeation was 97.8%. All the results indicated that the good surface conditions of the large-pore supports improved by the vacuum coating method were favorable for the formation of a compact MCM-48 membrane on it. (c) 2008 Elsevier B.V. All rights reserved.