We studied the effects of surface modification of bentonite with chitosan on its ability to adsorb Congo Red (CR) dye. The adsorption behavior of CR from aqueous solution onto raw (RB) and chitosan-modified (CMB) bentonite samples was investigated as a function of parameters such as initial CR concentration, contact time, pH and temperature. Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to confirm the surface modification. Compared with RB, the adsorption capacity of CMB for CR was greatly enhanced. Kinetic studies indicated that the adsorption of CR on both RB and CMB followed the pseudo-second-order kinetic model. From the thermodynamic parameters, the adsorption of CR on RB and CMB is spontaneous and endothermic. The results indicate that chitosan-modified bentonite provides an important advantage for CR dye adsorption over raw bentonite.