Novel amphiphilic biodegradable graft copolymer based on poly(aspartic acid) was prepared by attaching monomethoxy polyethylene glycol (mPEG) as hydrophiphic segment to poly(aspartic acid-g-octadecylamine) (PASP-g-ODA) as hydrophobic backbone. The chemical structures of amphiphilic copolymers were confirmed by FTIR and H-1 NMR spectroscopy. The polymeric micelles were prepared with solvent evaporation and their physicochemical properties in aqueous media were characterized by dynamic light scattering (DLS) and fluorescence spectroscopy. These micelles were confirmed to be pH-sensitive by measuring optical transmittance of micelle solution and the size of micellar aggregates. The number average diameter of polymeric micelles prepared in medium at pH 2.5 was larger than that in neutral and basic medium and showed a bimodal size distribution because of the protonation of carboxyl groups in backbone. Furthermore, the polymeric micelle can load water-insoluble drug (podophyllotoxin), and the drug release from micelles showed a pH-dependency. (c) 2005 Wiley Periodicals, Inc.