The aim of the present work was to investigate thiol-functionalized bentonite (TFB) as a novel adsorbent for the adsorption of As(III) from aqueous environments and to determine optimal adsorption conditions. The response surface methodology (RSM) was applied to analyze the most significant variables for adsorption including initial pH, temperature (degrees C, T), initial As(III) concentration (mgL(-1), C-o), adsorbent dosage (g, m) and contact time (min., t). The optimum adsorption conditions according to the RSM were found to be 5.98, 42.87 degrees C, 31.02 mgL(-1), 0.33g and 127.48 min for initial pH, T, C-o, m and t, respectively. Under these conditions obtained by the model, the maximum percentage of As(III) adsorption and adsorption capacity were found to be 91.01% and 8.56 mgg(-1), respectively. The kinetic studies showed that As(III) adsorption followed a pseudo-second-order kinetic model and the rate was controlled by both intraparticle and film diffusion. Experimental data were compared with linear isotherm models and it was found that the adsorption data has better fit to the Langmuir isotherm model. Furthermore, the thermodynamic studies showed that the adsorption of As(III) was endothermic, possible and natural. Based on all these conclusions, it can be said that TFB has high potential for As(III) removal from aqueous environments.