Pervaporative dehydration of acetic acid over the entire concentration range of 0-100% is studied using four copolymer membranes of acrylonitrile and high performance Nafion and polyimide membranes. From each copolymer of acrylonitrile, three different membranes were produced with three different copolymer compositions. Polyimide showed high water selectivity but very low flux, while Nafion showed highest flux but lowest selectivity. Copolymers of acrylonitriles showed reasonable flux and selectivity behavior. Among the acrylonitrile copolymers, copolymers with hydroxyethyl methylacrylate yielded water selectivity comparable to that of polyimide with much higher flux.