The Gibbs free energy of formation of BaThO₃ from elemental oxides has been measured at temperatures between 853 and 903 K using a CaF₂ solid electrolyte galvanic cell. The galvanic cell consisted of Pt, O₂, CaO+CaF₂∥CaF₂∥ BaThO₃+ThO₂+BaF₂, O₂, Pt EMF gave the standard Gibbs free energy for the reaction CaF₂+BaThO₃=CaO+BaF₂+ThO₂ as ΔG˚=123111.031-117.597 T (J/㏖).