[en] The electrochemical behavior of vanadium was studied with special reference to the formation and transformation of anodic oxide film. Below - 0.25V (S.C.E.), V₂O₄ film grew in a solution of pH 8.39. During film growth, the electric field within the film remained constant regardless of anodic current density. Above - 0.25V, however, vanadium dissolved as V (V), still keeping a thin V₂O₄ film on the surface. Air-formed V₂O₅ was unstable in aqueous solution and dissolved leaving V₂O₄. It was confirmed by coulometry that V₂O₄ film was electrochemically reduced to V₂O₂ or VOsub(0.53), and then to metallic vanadium. (auth.)