A new method for the electrochemical synthesis of oxide thick film in molten salt was developed. The following galvanic cell was assembled, and the electrolysis was carried out at 973 K Pt, metal(50-x/2) mole percent (m/o) KCl-(50-x/2) m/o NaCl-x m/o additive(O2-)YSZO-2, Pt where the additive was an oxide or a chloride containing the metal ions of the anode. When the additive was dissolved and ionized in the molten salt, its oxide film formed on the stabilized zirconia surface. At this time, metal ions derived from the additive were carried to the stabilized zirconia surface under an electric field, and reacted with oxide ions, coming from the oxygen electrode through zirconia solid electrolyte, to form the oxide film.