Sodium clinoptilolite-rich tuff from the Western Anatolia, Bigadic region was modified with octadecyltrimethylammonium bromide(ODTMA-Br) and hexadecyltrimethylammonium bromide (HDTMA-Br), and used for the first time to remove chromium(VI) from aqueous solution in a series of batch adsorption experiments. Various physico-chemical parameters affecting the adsorption process such as the contact time, pH, the optimum sorbent dosage and the initial concentration of chromium were studied. The Cr(VI) adsorption capacity of ODTMA- and HDTMA-treated clinoptilolite (Cp) was highly pH-dependent, and was found to be 3.65 mg/g and 2.85 mg/g at pH 2.0 and 3.0, and 0.25 g/50 mL sorbent dosage, 3 h equilibrium time and 25ºC, respectively. Langmuir, Freundlich and Dubinin–Radushkevich (D–R) models were applied to describe the adsorption isotherms. Langmuir’s model fitted the equilibrium data better than the Freundlich isotherm. From the D-R isotherm model, the mean adsorption energy (E) calculated as 15.075 and 14.744 kJ/mol for ODTMA-Cp and HDTMA-Cp sorbents showed that the adsorption of chromium occurred by chemisorption. The kinetic data indicated that the sorption of hexavalent chromium onto modified Cp followed well the pseudo-first-order kinetics. The current study considers that further developments in this line of research should continue to grow in the coming years, i.e., regarding water treatment, heavy metal and chromate removal using easily-available, low-cost microporous natural materials such as clinoptilolite.