Surface acetylation of cellophane to afford an asymmetric membrane having high desalination ability (as high as 98% sodium chloride rejection) is described. The films were characterized by multiple-internal-reflectance microscopy (MIR), dyeing tests, light microscopy, and determination of water and sodium chloride transport properties in reverse osmosis cells. Surface modification employing acetyl chloride and acetic anhydride was studied in detail: the influence of the cellophane employed, the degree of cellophane activation, reaction time, reagent concentration, and diluent were assessed. Mixed acetylation reactions are also discussed as well as an evaluation of various postconditioning treatments used to increase desalination.