In batch sorption experiments, particles and water are typically separated by centrifugation or filtration after sorption equilibrium has been reached. For hydrophobic (i.e., strongly sorbing) substances, incomplete separation of small, colloidal particles from water can lead to an overestimation of the truly dissolved concentration in water and thus to a significant error in the evaluation of sorption characteristics. In recent decades, equilibrium passive sampling methods using polymeric samplers such as a solid phase microextraction (SPME) fiber have been increasingly used for sorption studies. Passive sampling methods can avoid direct sampling of water and thus avoid experimental problems associated with phase separation. However, few studies have attempted to use a passive sampling method to investigate the sorption behavior of cationic surfactants. The purpose of this study was twofold: to investigate the equilibrium sorption of varying structures of cationic surfactants by kaolinite at relatively low solute concentrations; and to explore the possibility of using a SPME fiber passive sampling method to measure freely dissolved concentrations in kaolinite suspensions. To this end, batch sorption experiments were performed using a conventional batch-shaking and centrifugation method to determine sorption isotherms of five benzalkonium compounds (BACs) and two dialkyldimethylammonium compounds (DADMACs) on kaolinite. Both classes of cationic surfactants are widely used as disinfectants and preservatives.