Novel pH-sensitive graft copolymer of chitosan and poly(acrylic acid) (PAA) prepared by grafting acrylic acid onto maleoylchitosan using potassium persulfate as an initiator has been studied gravimetrically under nitrogen atmosphere in aqueous medium. The percentage grafting is favoured by increasing monomer concentration and reaction time but is affected by higher concentration of initiator and high temperature. The effects of the feed ratio of maleoylchitosan and AA on the properties of the copolymers, such as swelling ratio and pH-sensitivity, were determined. The swelling ratio of the copolymer was dependent on pH and weight ratio of poly(acrylic acid)/maleoylchitosan. FT-IR results indicated that copolymer was formed between poly(acrylic acid) and chitosan and the crystallinity of the copolymer was decreased. NMR and XRD were also used to characterize the copolymer. (c) 2006 Elsevier B.V. All rights reserved.