Ordered mesoporous MCM-48 membranes with cubic pore structure were prepared by solution growth method and characterized by XRD, SEM/EDS and unsteady-state gas permeation. The membranes were fabricated on symmetric alpha-alumina supports of different pore sizes under hydrothermal conditions using cetyltrimethylamonium bromide (CTAB) as a surfactant. The surfactant was removed by calcination and Soxhlet extraction at 100 degrees C using ethanol/HCl mixture. The X-ray diffraction showed that these membranes possessed a cubic MCM-48 pore structure. The N-2 adsorption studies at 77 K indicated high pore volumes and pore size distribution in the mesoporous regime with an average pore diameter of similar to 2.6 nm. The membranes prepared on the A15 alpha-alumina support (0.3 mu m average pore size) exhibited the presence of pinhole defects. The single gas N-2 and CO2 permeation experiments showed that the best quality membranes were synthesized on the alpha-A16 alumina supports (average pore size similar to 0.2 mu m) when the surfactant was removed by Soxhlet extraction. For these membranes the N-2 and CO2 permeation was found to be governed by Knudsen diffusion. The permeance, was independent of the feed pressure. indicating the absence of viscous flow contribution to gas transport. (c) 2006 Elsevier B.V. All rights reserved.