Batch adsorption experiments were carried out for the sorption of alpha and beta endosulfan onto bentonite clay. The effect of various experimental parameters such as contact time, adsorbent dosage, initial endosulfan concentration, pH and temperature was investigated. The equilibrium endosulfan concentrations were measured with GC/ECD. The equilibrium data were fitted to Langmuir, Freundlich, Dubinin-Radushkevich (D-R) and Temkin isotherm models and the isotherm constants were calculated for alpha and beta endosulfan. Five error functions namely ERRSQ, HYBRID, MPSD, ARE and EABS were applied to the isothermal equilibrium data in order to know the best fit isotherm model for the system. Kinetic studies were also undertaken in terms of pseudo-first-order, pseudo-second-order and intra-particle diffusion rates for alpha and beta endosulfan onto bentonite. The values of the thermodynamic parameters, i.e. enthalpy change (Delta H degrees), entropy change (Delta S degrees) and free energy change (Delta G degrees) were computed from the Van't Hoff plot of In K-D vs 1/T. (C) 2012 Elsevier B.V. All rights reserved.