The selectivity and the membrane flux depend on the textural and also on the chemical composition of the materiel used to prepare the membrane. The surface properties of gamma alumina membranes prepared by sol-gel route can be modified by grafting mono-, di- and tri-functional organosilanes (-OCH3, -OC2H5, -Cl) in the goal to change the selectivity of the membrane towards the chemical solutes. The characterization of the different membranes showed that the grafting depends on the nature of the silanes used and is achieved with the multifunctional silanes. The modification of the surface properties of the membrane prepared after grafting has been confirmed by pervaporation tests on different binary mixtures of solvents (water+ethanol, methylethylketone+cyclohexane, cyclohexane+ethanol). In these conditions, the flux of the different solvents and the selectivity of the membranes depends clearly on the grafting conditions. (C) 2003 Elsevier Science B.V. All rights reserved.