Poly(vinyl chloride)-graft-poly(butyl methacrylate), which was prepared by a radical graft polymerization of butyl methacrylate onto poly(vinyl chloride), and poly(vinyl chloride) itself were found to be effective permselective membrane materials for the selective separation of benzene from benzene/cyclohexane mixture in the whole feed composition range. The permeation rate was enhanced by the introduction of poly(butyl methacrylate) onto poly(vinyl chloride) membrane.