4-Vinylpyridine-homografted-polycarbonate (PC-g-4VP) membrane was prepared for water perselective pervaporation. The conditions of the chemical grafting reaction for synthesis PC-g-4VP were studied in terms of the reaction time, reaction temperature, monomer concentration, and the concentration of initiator in the reaction. The effect of feed composition, degree of swelling, and operation temperature on the pervaporation performances were investigated. It was found that water permeated through the PC-g-4VP membrane perferential in all range of feed compositions. The permeation rate and separation factor increased with increasing 4-vinylpyridine content in the membrane. PC-g-4VP membrane effectively improved both the water permeation rate and water-ethanol separation factor of the unmodified polycarbonate membrane. The total permeation rate of PC-4-VP membrane with 26.7% degree of grafting was 153 g/m(2) h, and the separation factor was above 6300 for a 90 wt % aqueous ethanol feed solution.