Graft copolymers of poly(ethylene glycol) (PEG) on a chitosan backbone (PEG-g-chitosan) have been synthesized and their aqueous solution properties were investigated. At pH 6.5 the graft copolymers are 100% soluble, while chitosan phase separates from solution at those conditions. These interesting graft copolymers may be especially suitable as carriers for delivery of anionic drugs, such as proteins, glycosaminoglycans, and DNA plasmids or oligonucleotides.