Cation exchange capacity (CEC) is one of the fundamental properties of clays and provides a means for estimating the general chemical properties of clays. The ammonium acetate saturation and sodium saturation methods are commonly used for measuring CEC. However, both methods are experimentally quite difficult and time consuming. This study investigates the feasibility of using cationic surfactant adsorption to determine the CEC of, an expandable clay, montmorillonite. Two laboratory grade montmorillonite samples with CEC of 71 (montmorillonite A) and 22 (montmorillonite B) mmol/100 g respectively were used in this study. Experimental results indicate that benzyltriethyl ammonium (BTEA) ion with an effective number of CH2 groups in hydrocarbon chain of 5–7 should be used to provide reasonable estimations for monolayer capacity and CEC. The method has advantages compared to traditional methods in that it is simple and can easily be applied without the requirement for specialized equipment.