This research involved the efficient adsorption of an anionic dye (Reactive Red 120) by natural untreated clay, a low-cost material abundant in highly weathered soils. The adsorption kinetics was investigated using the parameters such as contact time, stirring speed, initial dye concentration, initial pH, ionic strength, and solution temperature. According to these experiments the maximum removal is observed after 80 to 100 min. The results showed that acid pH is favorable for the adsorption of dye and physisorption on broken edges of clay particles seemed to play a major role in the adsorption process. It was found that the rate of adsorption decreases with increasing temperature and the process is exothermic. The adsorption kinetics followed the pseudo-second-order equation for the dye investigated in this work. Furthermore the thermodynamic activation parameters such as the enthalpy and entropy were determined. Compared to adsorption experiments on other clays, the results show that the Fouchana natural clay is an efficient adsorbent for Reactive Red 120 dye. (C) 2011 Elsevier BM. All rights reserved.