Abstract: The poly( lactic acid) / ethyl cellulose composite films were prepared by a casting method using n-alkenylsuccinic anhydride( ASA) as novel plast icizer and chlor oform as co-solvent. Fourier transform infr ared spectroscopy( FTIR) and X-r ay diffraction (XRD) were used to analyze the morphological pr operties of the composit e films. Themechanical proper ties and water absor ption of the cast composite films were also measured. FTIR indicates thatther e are some strong inter action and good compatibility in the composite films. XRD shows that both poly( lact icacid) ( PLA) and ethyl cellulose ( EC) lose cr ystallinity after being plast icized, and the PLA/ EC composite filmsplast icized with n- ASA r esult in a markedly enhanced coalescence of the two polymers. The mechanical proper tieswer e t ested and n- ASA becomes an ideal plast icizer for EC based films. The PLA r esin has a reinforcing effect onPLA/ EC composite films when the mass f raction of PLA is less than 37%. The water absorption decreases withincr easing ASA content while it increases with incr easing PLA content in the PLA/ EC composite films. Thecomposite films can be used as a new kind of drug delivery materia l with a wide application pr ospect.