Ordered mesoporous nickelsilicate catalytic membranes have successfully been synthesized on the surface of gamma-alumina disk and alpha-alumina tube by dip coating and immersion. The surface of the supports was cleaned and chemically modified by a series of aqueous solutions. The resulting films and bulk materials have been characterized by XRD, N-2 adsorption-desorption, SEM and TEM. Gas permeation testing was carried out in a Wicke-Kallenbach cell to evaluate the separation properties of the synthesized membranes. The formation, morphology and permeation properties of the membranes have been correlated with the nature of the alumina supports, their surface treatment, and conditions of the hydrothermal synthesis. The lower permeance for oxygen molecules has been explained by a chemical effect. The different permeance between methane and propane through the membranes results most probably from the different diffusion constraints of the two molecules, i.e. a physical effect. (C) 2003 Elsevier B.V. All rights reserved.