This work has demonstrated that the novel chitosan derivative, synthesized by phase transition and grafting diethylenetriamine, has a great potential for the adsorption of acid dyes from aqueous solutions. Four acid dyes with different molecular sizes and structures were used to investigate the adsorption performance of diethylenetriamine-modified chitosan beads (CTSN-beads). Results indicated that the adsorption of dyes on CTSN-beads was largely dependent on the pH value and controlled by the electrostatic attraction. In addition, the adsorption rate (AO10>AO7>AR18>AG25) and adsorption capacities (AO7>AR18>AO10>AG25) were directly related to the molecular size of the dye and the amount of the sulfonate groups on the dye molecules. The equilibrium and kinetic data fitted well with the Langmuir-Freundlich and pseudo-second-order model. Furthermore, thermodynamic parameters indicated that the adsorption processes occurred spontaneously and higher temperature made the adsorption easier. The reuse tests indicated that the CTSN-beads can be recovered for multiple uses. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4090-4098, 2013