The pervaporation separation of water-alcohol mixture was carried out using grafted terpolymer membrane at -10-50 degrees C. PVA-g-ST/MA-Hz (III) terpolymer was prepared by graft copolymerization of styrene (ST)-maleic anhydride (MA) hydrazine (Hz) copolymer (ST-co-MA-Hz) (II) onto poly(vinyl alcohol) (PVA) by a condensation-coupling reaction through esterification that was performed between the hydroxy groups of PVA and the anhydride groups of ST-co-MA-Hz (II) copolymer. The ST-co-MA-Hz (II) copolymer was prepared by the chemical reaction of ST-co-MA (I) and Hz in dioxane. The ST-co-MA (I) copolymer was prepared by the copolymerization of MA and ST in dimethyl sulfoxide (DMSO) by using azobisisobutyronitrile (AIBN) as an initiator.In order to obtain a membrane high in both selectivity and permeation rates, a series of PVA-g-ST/MA-Hz were synthesized with different compositions. Water was permeated through membrane preferentially in all ranges of water-alcohol feed compositions in this study. The permeation rate decreased and the selectivity increased as the PVA content in membrane rose. The effects of the molecular size of the permeating species on both permeation and separation were also investigated.