chitosan film exhibited pH sensitive effect and the highest swelling appeared at pH 7 and 8.Chitosan is a week base with a pKa value between 6.0 and 6.5.The tested minimum water uptake capacity occurred at pH = 6.0which is near the isoelectric point. At this point, cations and anions reach equilibrium. As pH of the solution increased or decreased near the isoelectric point, protonation of NH2 and deprotonation of OH caused the chitosan films to swell. Further increased or decreased of solution pH, the adding Na+and Cl−ions for adjusting pH would strengthen the shielding effect and cause the chitosan films to shrink