Adsorption of Acid Orange 8 onto surfactant-modified clinoptilolite was studied conducting batch experiment system. Effect of pH, dye concentration and contact time on the adsorption was evaluated. Equilibrium adsorption data were analyzed by Langmuir, Freundlich, Redlich-Peterson and Koble-Corrigan isotherm equations using nonlinear regression analysis. The adsorption was analyzed using pseudo-first-order and pseudo-second-order kinetic models and pseudo-second-order model provided the best correlation of the experimental data. Adsorption process was found to be controlled by both surface and particle diffusions. (c) 2006 Elsevier Ltd. All rights reserved.