Hybrid monolayers of a clay mineral and an amphiphilic alkylammonium (octadecylammonium) cation have been prepared by spreading the alkylammonium cation onto surfaces of clay suspensions. π–A isotherm curves at various clay concentrations indicate that the floating monolayers of the amphiphilic alkylammonium cation are hybridized with clay platelets at an air–clay suspension interface, and that the density of the alkylammonium cation in the hybrid monolayer is dependent on the concentration of the clay in the suspension. The hybrid monolayers were deposited on glass surfaces by horizontal dipping to form hybrid multilayers. The p-polarized infrared external reflection spectra of the hybrid multilayers show that the alkyl chains of the alkylammonium cations in the film are almost perpendicular to the film surface. According to the X-ray diffraction data of the multilayers, the thickness of a unit layer (one clay layer and one alkylammonium cation layer) decreases with the increase in the clay concentration in the suspension used for the film preparation. A model of a layered structure of the hybrid multilayer has been proposed.