This work investigated the sorption performance of the ethylenediamine modified starch (CAS) for the removal of acid dyes from aqueous solutions. The influence of pH on adsorption of acid orange 10 (AO10). acid green 25 (AG25) and amido black 10B (AB10B) was evaluated. The sorption kinetics, equilibrium uptake and desorption of the loaded dyes in sodium sulfate solution were studied. It was found that the interaction mechanism was based on electrostatic attraction and hydrogen bonding. The adsorption of AG25 and AB10B followed pseudo-second-order model, whereas AO10 followed both pseudo-first-order and pseudo-second-order models. The best isotherm was Langmuir equation and the capacities followed the sequence AB10B > AC25 > AO10. The different behaviors of individual dyes adsorption on CAS were largely dependent on the number of hydrophilic functional groups, which had strong tendency to form hydrogen bonds with the biosorbent. Dye release in sodium sulfate solutions was determined by the salt concentration and nature of dyes. (C) 2009 Elsevier B.V. All rights reserved.