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In this study, the adsorption mechanism of cetyltrimethylammonium bromide (CTAB), a cationic surfactant, to a clayey soil from aqueous solution was investigated as a function of ionic strength, pH, temperature, CTAB equilibrium concentration, and stirring speed. In addition, both kinetics and thermodynamic evaluations of the adsorption data were supported with measurements of particle zeta potential and suspension electrical conductivity. The amount of cetyltrimethylammonium bromide adsorbed to clayey soil increased with increasing CTAB equilibrium concentration, temperature and ionic strength, but was not affected from pH and stirring speed. The isosteric enthalpy and entropy changes were calculated as 28.27kJmol⁻¹ and −0.091kJmol⁻¹K⁻¹, respectively. This positive enthalpy value indicates that the adsorption process was endothermic. The negative and quite small isosteric entropy change indicates …