Bentonite was found to have adsorption capacity for Pb(II), Cr(III), Zn(II) and Co(II). Towards this aim, batch adsorption experiments were carried out and the effects of various parameters (solution pH, dose of bentonite loading, contact time, temperature, and initial metal concentration) on this removal process have been investigated. Adsorption was decreased with increasing temperature for all studied metals. The Langmuir and Freundlich adsorption models were used for mathematical description of the adsorption equilibrium. Equilibrium data was fitted to the Langmuir model in the concentrations of 10-100 mg L-1 at 293 and 313 K. Based on the Langmuir isotherm plots, the maximum adsorption capacity value was calculated to be 30.40 mg g(-1) for Cr(III), 30.27 mg g(-1) for Pb(II), 29.94 mg g(-1) for Zn(II), and 29.85 mg g(-1) for Co(II), at 293 K. Various thermodynamic parameters, such as Delta G degrees, Delta H degrees, and Delta S degrees, were evaluated with results indicating that this system was an exothermic spontaneous reaction and kinetically suited to pseudo-second order model. Adsorption ability of bentonite decreased in the order of Cr(III) > Pb(II) > Zn(II) > Co(II), and its adsorption capacity in the order of ZnCl2 activation > NaOH activation > H2SO4 activation > native bentonite.