The novel amphoteric, pH-sensitive, biodegradable poly ([chitosan-g- (L-lactic-co-citric) acid]) hydrogel (CLC) was synthesized through the reaction of chitosan (CS) with poly(L-lactic-co-citric acid) (PLCA). The structure of CLC was characterized by Fourier transform infrared spectroscopy, elemental analysis, and wide-angle X-ray diffraction measurement. The degree of substitution of CS amino groups was evaluated from salicylaldehyde analysis. The swelling behavior of CLC film in an aqueous solution with various pHs and the apparent swelling kinetics were studied. The swelling mechanisms of CLC film in acidic and alkaline mediums are discussed. The results showed that CLC hydrogel had a higher degree of swelling in the pH range of 4 > pH > 8 and that the swelling rate order in different buffers was neutral > acidic > basic mediums. (C) 2003 Wiley Periodicals, Inc.