Pervaporation of an acetic acid/water mixture was studied through synthetic polymeric membranes made from poly(1-butyl methacrylate), poly(2-ethylhexyl methacrylate), polystyrene, and copolymers of 4-vinylpyridine and styrene, whose mole fraction of 4-vinylpyridine was 0.028 or 0.060. Permselectivities through polystyrene and poly (4-vinylpyridine-co-styrene) (mole fraction of 4-vinylpyridine, 0.050) are discussed based on the solution-diffusion theory.