Adsorption of Congo red (CR) from water via batch adsorption experiments onto bentonite and CTAB-modified bentonite (CTAB-MBn) was investigated. Studies concerning the factors influencing the adsorption capacities of bentonite and CTAB-MBn, such as initial dye concentration, adsorbent dosage, pH, ionic strength, contact time and temperature were systematically investigated and discussed. The results revealed that CTAB-modified bentonite demonstrated high adsorption capacities toward acid dyes, while bentonite exhibited sorption capacities lower than CTAB-MBn. The kinetics data were analyzed using first order and pseudo-second order models. It was best described by the pseudo-second order model. The isotherm data were investigated accord¬ing to Langmuir and Freundlich equations. Thermodynamic parameters ΔG°, ΔH° and ΔS° were calculated for the adsorption of CR on bentonite and CTAB-MBn ; the value of ΔG° showed the spontaneous nature of adsorption for both sorbents.