The structure of the Langmuir-Blodgett (LB) films composed of cadmium stearate and poly(vinyl octanal acetal) has been investigated by the interlayer energy transfer (ET) method and transmission electron microscopy (TEM). The energy transfer efficiency from an energy donor to an acceptor, both being covalently linked to the polymer layers, was measured to examine the thermal relaxation process of the composite LB film. The ET method is very sensitive to the alteration of layer distance, i.e., to the microscopic structural relaxation of the layered structure. The layered structure in the LB film was lost at the melting temperature (T-m) of the stearate layers. The disordering process proceeded irreversibly, and the heat treatment above the melting temperature T-m made the structure completely destroyed within a few minutes. Different types of disordered structures were observed by TEM in three temperature ranges. Heating at temperatures lower than T-m yielded wrinkles of the film, but no aggregation of cadmium salt was observed. At a temperature near T-m, the crystalline structure of cadmium stearate grew gradually. At a temperature higher than T-m, cadmium stearate completel y dissolved and two distinct phases were observed in the TEM image, one corresponding to the polymer chain stained with cadmium and the other corresponding to cadmium stearate. Several hours were required for the occurrence of the structural change in the scale observed by TEM. The structural relaxation process of cadmium stearate LB films could be determined clearly by the ET method and TEM observation.