Different membranes which permeate water selectively from water-ethanol mixtures were prepared by plasma graft-polymerization of styrene onto porous poly(vinylidene fluoride) (PVDF) films, by sulfonation of the grafted membranes, and by ionization of the sulfonated membranes, respectively. The permselectivities of the grafted (g-PS), sulfonated (g-PSS) and sodium salt form of sulfonated (g-PSS-Na+) membranes were investigated in view of the feed composition of the water-ethanol mixture and the grafted amount of polystyrene (PS). It was found that the permselectivity increased with the ethanol concentration in the feed and that the grafted amount should be controlled for optimum separation of water. The g-PSS-Na+ membrane with a grafted amount of PS of 0.14 mg/cm(2) was found to have a high permeation rate of 6.6 kg/m(2)h, and a separation factor of 21 for the pervaporation of aqueous 60 wt% ethanol solution at 50 degrees C.