In order to develop organic magnetic thin films, we carried out a structure study of the Langmuir-Blodgett (LB) multilayers of transition metal ion-fatty acid salts using X-ray diffraction. We found that the LB films of manganese n-eicosanate exhibit a most feasible system for the magnetic thin film due to their stability and reproducibility. The LB film with the multiplicity less than three layers shows that fatty acid molecules align perpendicular to the substrate surface. On the other hand, layers more than four exhibit the tilt orientation of ca. 30 degrees along the layer normal to the substrate. Uniformity of the crystalline size in the LB film plane was found to be high so that the well-defined precision of molecular arrangement holds along the film normal to the substrate. We concluded that the structure presented here coincides well with the findings obtained from electron paramagnetic resonance and other spectroscopies.