An amphiphilic unsymmetrical merocyanine forms J- and H-aggregates by changing molecular environments in the binary and the ternary mixed monolayer assemblies, which have been characterized by visible absorption spectra films having red-shifted and blue-shifted bands in comparison with the solution spectrum, respectively. From the surface pressure-area isotherms of the mixed monolayers, the film structures were studied at the air/water interface. The in-plane X-ray diffraction and the atomic force microscopy measurements of their LB films were done to observe the fine lattice structure. The aggregate structures were well corresponding to the dye arrangements speculated by calculation with an extended dipole model for the spectral shifts. (c) 2005 Elsevier B.V. All rights reserved.