Abstract: Pervaporation is a membrane separation process which can be used to fractionate liquid mixture. In this paper the mechanism of pervaporation is described. The separa-tion of ethanol-water mixture by pervaporation is of great importance for the produc-tion of ethanol from biomass. The membranes for separation of ethanol water mixture can be divided into two types:hydrophilic and hydrophobic. Some physical methods have been used to improve the pervaporation process. The tendency of development of pervapration membranes, as indicated by author, is from homogeneous, asymmetric to composite membrane.