N,N-dimethylaminoethyl methacrylate was graft-polymerized onto the porous polypropylene films of Celgard 2400 and 2500 which have been previously surface-activated by glow discharge plasmas. The grafting was dependent on various factors both in the plasma pretreatment and the post-polymerization with the monomer. The reaction was discussed from the aspects of the dependences of graft polymerization on discharge power, plasma pretreatment period, etc. When the grafting exceeded a critical amount depending on the size of pores on the substrate film, pervaporation of water-ethanol separation functioned through these grafted membranes. The water permselectivity was improved by the ammonium ionization of the pendant N,N-dimethylamino group using dimethyl sulfate or chloroacetic acid, although the increase of prevaporation performance was not so high as those previously obtained by the grafted poly(sodium acrylate) -type membranes. Pervaporation characteristics of these membranes were discussed from the ionized states of the permselective layers analyzed by IR and ESCA.