The formation process of metallic Langmuir film on the water surface fabricated from BEDO-TTF (BO) and stearic acid (SA) is described. The in-situ observation by Brewster angle microscope revealed a creation of small islands after spreading the mixing solution on the water surface and then a formation of homogeneous Langmuir film by a coalescence of the islands with decreasing of the surface area. An appearance of mixed valence state of BO in both islands and Langmuir film was confirmed by polarization-modulated IR reflection absorption spectroscopy. A theoretical simulation of the spectra supports the bilayer model on the water surface, in which a metallic BO layer underlies between the SA layer and the water surface. An investigation on the Langmuir-Blodgett (LB) films transferred onto substrates by infrared spectroscopy implies the existence of hydrogen-bonded carboxylate groups of (R-COO . . .H . . . OOC-R)(-) in the SA layer. Finally, the optical conductivity in the LB films can be compared with those of the superconductor crystal (BO)(2)ReO4(H2O) through the Drude optical parameters obtained from the IR spectra fitting.