Adsorption of cationic surfactants onto clay is of interest in cosmetic applications as well as in environmental issues. Adsorption of alkyl(C-13-15) benzyldimethylammonium chloride (ABDAC) onto montmorillonite-type clay is investigated in this work. Variation in the concentration of exchangeable cations of the clay in solution as a function of the amount of ABDAC adsorbed showed the adsorption process to be controlled by the surface charge density of the clay. Basal spacing of the clay increased stepwise by 7 Angstrom during the adsorption process, indicating a final bilayer arrangement within the interlayers. Surface compaction of the alkyl chains determined by IR absorption at 2912 Angstrom were in full agreement with the variation in specific reduced surface excess n(1)(sigma(n))/m Enthalpy of desorption of water from organo-clay complexes showed the surfaces to be hydrophobic even at low surface coverage, owing to flat-lying alkyl chains.