Pervaporation is a promising technique with significant potential in a wide range of applications, such as the dehydration of organic compounds, the recovery of organic compounds from water and the separation of organic mixtures, and provides several advantages: easy process design, high selectivity, low energy consumption and moderate cost to performance ratio etc. In the present work, a study of the pervaporation separation of ethylacetate/water mixtures of low percentages of ethylacetate was carried out using organic–inorganic composite membranes on the porous alumina support. The organic–inorganic composite membranes were prepared by a cross linkage reaction of the hydroxyl groups of poly(dimethyl siloxane) (PDMS) and the Si–H bonds of poly(methyl hydrogen siloxane) (PMHS). The pervaporation membrane possesses the high selectivity for ethylacetate transport (a = 40–140) and a high ethylacetate flux (Q = 0.7–1.50 kg/m2h). The effects of the thermal treatment for PDMS/PMHS membrane on the existence of silanol and methyl groups, and flux and separation factor are discussed.