When a benzene/cyclohexane mixture was permeated through poly (dimethyl acrylamide-random-methyl methacrylate) (DMAA-r-MMA) and poly (dimethyl acrylamide)-graft-poly (methyl methacrylate) (DMAA-g-MMA) membranes by pervaporation, the benzene-permselectivity of the DMAA-r-MMA membrane changed from the diffusivity selectivity to the solubility selectivity with increasing DMAA content but DMAA-g-MMA membranes with a high DMAA content had the higher apparent diffusivity selectivity than the apparent solubility selectivity. Furthermore, the apparent solubility selectivity for a benzene/cyclohexane mixture between the DMAA-r-MMA membrane and the DMAA-g-MMA membrane with a high DMAA content was remarkably different. These results were attributed to the difference of structure between the copolymers.