In this paper, a batch system was applied to study the adsorption behavior of methylene blue (MB) on modified clinoptilolite. A desilication process involving NaOH treatment was carried out to obtain modified clinoptilolite with improved accessibility and molecular transport by widening the pores. Modification of clinoptilolite by alkaline treatment was investigated by various characterization techniques such as X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), X-ray photoelectron (XPS) spectroscopy, thermogravimetric/differential thermal analysis (TG/DTA), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and N-2 gas adsorption-desorption techniques. The effects of pore size and Si/Al ratio on the adsorption capacity were examined by varying the experimental parameters (initial pH, dye concentration, temperature, adsorption time and ionic strength of medium) to find optimum conditions that result in high adsorption capacity for MB removal. Maximum dye uptake was found to be 47.3 mg/g, which is similar to 47% higher that of raw clinoptilolite, indicating that desilicated clinoptilolite is an efficient adsorbent for MB. All the results showed that adsorption capacity for MB can be greatly improved through increasing the mesoporosity of parent clinoptilolite by desilication. (C) 2011 Elsevier Inc. All rights reserved.