The graft copolymer, chitosan-g-poly (ethylene oxide), was prepared through graft polymerization of poly (ethylene oxide) chains to chitosan due to the reaction between OH groups from poly (ethylene oxide) and COOH groups from 6-O-succinate-N-phthaloyl-chitosan (PHCSSA) in the presence of water as a swelling agent. The product particles are spheres with the size of few hundred nanometers as observed from transmission electron micrographs. Then phthaloyl groups were deprotected to give the free amino groups. The chemical structure of chitosan-g-poly (ethylene oxide) was characterized by FTIR, H-1 and C-13 NMR spectroscopies. XRD, Spectrofluorophotometry and TEM were also used to characterize the copolymer. (c) 2005 Elsevier B.V. All rights reserved.