We report the adsorption study of two commercial dyes, Acid Red 18 (AR18) and Acid Yellow 23 (AY23), onto bentonite based composite adsorbent from aqueous solution. The modified bentonite adsorbent was developed with the expectation to better adsorb anionic dyes. Single dye adsorption equilibrium was measured and the experimental data was analysed by the Langmuir, Freundlich and Redlich-Peterson isotherms. The results indicate that the Redlich-Peterson model provides the best correlation of the experimental data. The adsorption capacities estimated from the Langmuir model for AR18 and AY23 were at 69.8 and 75.4 mg/g, respectively. Binary dye adsorption was also investigated. The results reveal that the multicomponent nature of the dye wastewater introduces additional complications to the adsorption process. Many new factors need to be taken into account, including the interactions between the adsorbate molecules, the variation in adsorption affinity, and the fraction of adsorption sites being shared by each adsorbate. (c) 2009 Elsevier B.V. All rights reserved.