Hydrophobic organic-inorganic composite membranes with cross-linked poly(dimethyl siloxane)-poly(methyl hydrogen siloxane) (PDMS/PMHS) were prepared on a porous alumina tubular support. The PDMS/PMHS polymer penetrated into and plugged the pores of the gamma-alumina support. The membrane had an approximately 3.5-mu m-thick polymer/alumina composite layer. The alumina matrix inhibited the swelling of the PDMS/PMHS membrane. The pervaporation separation of an ethylacetate/water mixture with low percentages of ethylacetate was carried out with these composite membranes. The effect of the thermal treatment of the PDMS/PMHS membrane on the existence of silanol and methyl groups, and the flux and separation factor were investigated. The flux and separation factor were varied depending on the temperature of thermal treatment of the PDMS/PMHS membranes. (C) 2009 Elsevier B.V. All rights reserved.