Abstract: Three types of composite PDMS membranes were prepared by using PAN, CA, and PVDF as support materials and used to separate ethanol from aqueous solution by pervaporation.The experimental results evidently demonstrated that the support layer had a significant impact on the flux and selectivity of composite PDMS membranes. The effect of the average pore size of supports on the performance of composite PDMS membranes was complex, and depended on many factors such as the physico-chemical properties of skin layers or supports and the preparation methods of composite membranes. The total flux of ethanol-water mixture through each composite PDMS membrane increased with increasing temperature. In contrast, the relation between selectivity and temperature was different due to various supports. With increasing feed concentration, the flux through each composite PDMS membrane increased quickly while the selectivity decreased.All these observation would be helpful to provide a guideline for the selection of an optimum support layer.