Chitosan hydrogel beads were modified with ammonium sulfate to remove a dye (Acid Orange-7) in aqueous solutions at pH 8.2. The modified beads present much higher sorption capacity than the native beads in the basic solution. The sorption equilibrium was measured in a batch adsorber, and kinetics was investigated in a fixed bed rig. The breakthrough curves were found to be J-shaped in general and were modeled by the Wheeler-Jonas equation with a two-segmented approach. Analysis shows that the kinetics is controlled by film resistance and intraparticle diffusion in each segment, respectively.