The structures of Langmuir-Blodgett films of cadmium soaps have been investigated using grazing incidence synchrotron X-ray diffraction and imaging plate detection. It was found that the cadmium atoms in the films are arranged with a monoclinic (C) symmetry, while the chains have the same monoclinic structure as that of the metal atoms but without the centered symmetry. The chains are perpendicular to the film surface and arranged in a herringbone pattern. For the first time with X-ray diffraction, a 5 x 1 superstructure present in the film plane and commensurate with the local structure was observed. The meridional diffraction shows a pattern from a set of wide slits, from which thicknesses corresponding to both a monolayer and a bilayer of the cadmium soap films were determined.