The adsorption of Cr(VI) onto waste acorn of Quercus ithaburensis was studied using fixed-bed adsorption. The experiments were conducted to study the effect of important design parameters such as flow rate, solution pH and particle size of adsorbent. Decrease in adsorbent particle size and flow rate produced a better bed capacity. Also an increase in flow rate and particle size resulted in a decrease in the bed volumes at the breakthrough. The highest bed capacities of fixed-bed column were obtained at pH 2.0. In the beginning of all the pH experiments, the effluent pH increased dramatically and then dropped and approached lower values. The breakthrough data obtained for Cr(VI) was adequately described by the Thomas and Yoon-Nelson adsorption models. Good agreement between the predicted theoretical breakthrough curves and the experimental results were observed. This study indicated that the waste acorn of Quercus ithaburensis can be used as an effective and environmentally friendly adsorbent for the treatment of Cr(VI) containing wastewaters. (c) 2006 Elsevier B.V. All rights reserved.