This work was performed to study the characteristics of electrochemical intercalation reactions occurring at the interface between the organic electrolyte and tungsten trioxide thin film (thickness of 4000Å) prepared by e-beam evaporation method as cathodically coloring oxide with regard to the electrochromism by the intercalating reactions of the lithium cation in the 1M LiClO₄/PC organic solution. The characteristics of electrochemical intercalation reactions were investigated by various DC electrochemical methods such as cathodic Tafel polarization test, multiple and the single sweep cyclic voltammetry and the coulomety titrations method. The surfaces of thin films were observed with the patterns of X ray diffraction after the coloring and bleaching reactions. In comparison with the previous results that WO₃thin film intersely detached from the surface of electrode when the hydrogen cation was intercalated into WO₃ thin film in the o.1N H₂SO₄ aqueous solution, the intercalation reaction of lithium cation into WO₃ thin film in the 1M LiClO₄/PC organic solution was shown that the stable bleaching and coloration was appeared within 1.0V of the applied overpotential. When the overpotential of electrochromic reaction for lithium cation in the 1M LiClO₄/PC organic solution had been applied up to 1.5V, the accumulation phenomenon of lithium in amorphous WO₃ thin film layer occurred because the inserted lithium into amorphous WO₃ thin layer for coloring process was not fully removed from the thin layer to the electrolyte during bleaching process. It was found that there is a limitation of applied overpotential for coloring process by the reduction of the current densities of bleaching and coloration after few number of coloring and bleaching cycles.