Poly(methacrylic acid)-grafted chitosan membranes (chito an-g-poly(MAA)) were prepared in two sequential steps: in the first step, chitosan membranes were prepared by phase-inversion technique and then epichlorohydrin was used as crosslinking agent to increase its chemical stability in acidic media; in the second step, the graft copolymerization of methacrylic acid onto the chitosan membranes was initiated by ammonium persulfate (APS) under nitrogen atmosphere. The chitosan-g-poly(MAA) membranes were first used as an ion-exchange support for adsorption of trypsin from aqueous solution. The influence of pH, equilibrium time, ionic strength, and initial trypsin concentration on the adsorption capacity of the chitosan-g-poly(MAA) membranes have been investigated in a batch system. Maximum trypsin adsorption onto chitosan-gpoly(MAA) membrane was found to be 92.86 mg mL(-1) at pH 7.0. The experimental equilibrium data obtained for trypsin adsorption onto chitosan-g-poly(MAA) membranes fitted well to the Langmuir isotherm model. The adsorption data was analyzed using the first- and second-order kinetic models, and the experimental data was well described by the second-order equation. More than 97% of the adsorbed trypsin was desorbed using glutamic acid solution (0.5M, pH 4.0). In addition, the chitosan-gpoly(MAA) membrane prepared in this work showed promising potential for various biotechnological applications. (C) 2007 Wiley Periodicals, Inc.