The use of montmorillonite and its modified forms as an adsorbent in aqua system have been widely considered but the scope of much of the works has been restricted to batch tests, which may be a mean of selecting the best adsorbent for a given application but not necessary how it would be used in practice. This paper, therefore, deals with the comparison of batch and fixed bed adsorption of methylene blue (C16H18ClN3S) by montmorillonite and its derivatives. The modified clays were prepared by altering the surface properties of the raw montmorillonite clay, from organophobic to organophilic, with four types of quaternary ammonium compounds (QACs). They are tetramethylammonium chloride (C4H12ClN), tetradecyltrimethylammonium bromide (C17H38BrN), hexadecyltrimethyl ammonium bromide (C19H42BrN), and benzyldimethylhexadecylammonium chloride (C25H46ClN), which are different in their molecular size and number of carbon atoms. The clay products, namely organo-clays, were characterized for their physical properties by BET surface analysis, particle sizing, and X-ray diffraction (XRD). Adsorption experiments of methylene blue were performed by batch and fixed bed column techniques. The objective of the batch test is to determine the effect of the number of carbon atoms in QACs used for the preparation of organo-clays on their physical properties and also on the adsorption affinity of each clay towards the methylene blue. For the column experiments, mixed sand-clays bed was used due to the fine particle size of clays. The effect of adsorbate flow rate, contact time, and the initial concentration of the solute were explored. The permeability of the mixed sand-clay bed was also studied. The results showed that the permeability of the mixed bed was decreased considerably in the presence of even small amount of clays. Batch results were well characterized by a Langmuir isotherm. Column results were correlated by Fornwalt and Hutchins method. (C) 2004 Elsevier B.V. All rights reserved.