Langmuir-Blodgett films, incorporating N-sulphopropyl substituted thiadicarbocyanine dyes with a fixed polymethine chain adsorbed on octadecylpyridinium monolayer, have been prepared. Dye molecules in Langmuir monolayers form J-aggregates, which structures depend on monolayer preparation conditions. The dyes also form mixed J-aggregates. The film structure has been studied by using X-ray small-angle diffraction and spectroscopy. It was shown, that optical anisotropy of J-aggregated dye films is related to the conditions of monolayer transfer onto solid supports.