We report on the photophysical application of the multilayer films of an ion-exchange adduct of a clay (synthetic saponite) and an alkylammonium cation (trimethylstearylammonium) as prepared by the Langmuir-Blodgett method. For preparing a film, the adduct was dispersed in chloroform and spread over the surface of pure water. A surface pressure-area isotherm was obtained at 25.0 degrees C with complete reproducibility. The critical surface area, A(c), was defined as an area where the linear portion of the isotherm was extrapolated to zero surface pressure. From the dependence of A(c) on the spread amount of the adduct, it was concluded that the adduct formed a film of a single clay layer at an air-water interface. The floating film was transferred onto a hydrophilic glass substrate or a calcium fluoride plate as a Z-type multilayer film. The film was characterized by X-ray diffraction, infrared absorption spectra, and atomic force microscopy images. The prepared clay film was revealed to act as an efficient barrier for the occurrence of photoinduced electron transfer from an amphiphilic polypyridyl-Ru(II) complex (electron donor) to an amphiphilic acetylacetonato-Ru(III) complex (electron acceptor).