The adsorption of reactive yellow 145 (RY145) dye onto chitosan 8B in aqueous solution was investigated using batch method. Experiments were carried out at various pH, initial dye concentrations, ionic strengths and temperatures. The suitable pH was found to be 4 among the observed pH ranges between 4 and 11. The maximum amount of dye uptake onto chitosan 8B was found to be 129.87 A mu mol/g at 30 A degrees C. Adsorption kinetic data acquired from various batch experiments were examined using pseudo-first-order, second-order, Elovich, intraparticle, and film diffusion kinetic models. The results revealed that the sorption process follows pseudo-second-order kinetics, whereas film diffusion and intraparticle diffusion are the rate-limiting steps. Freundlich, Temkin and Langmuir models were used to analyze the equilibrium sorption data. Langmuir model shows higher consistency than the other two models. The computed values of activation and apparent thermodynamic parameters confirm the conclusion that the adsorption of RY145 molecules onto chitosan 8B in aqueous solution is an endothermic spontaneous-physisorption process.