Poly (acrylic acid)-modified chitosan amphiphilic gels were prepared ,via, O-maleoyl-N- phthaloyl- chitosan as an intermediate by grafting with poly (acrylic acid). The reaction was carried out in a homogeneous system by γ-ray irradiation. Evidence of grafting was obtained from FTIR spectroscopy. The effects for grafting reaction were investigated systematically. Results show that the grafting degree depends on monomer concentration and absorbed dose. The swelling behavior of chitosan samples with different grafting degree was studied in different buffers as a function of pH. It can be found that all the samples swollen slightly at low pH but very well at high pH. Moreover, the swelling behavior of chitosan samples in DMF has been evaluated.