Employing the electrochemical cells with the solid oxide electrolyte Kanthal + Re, Te(1), TeO2(s)parallel to O(-2)parallel to air, Pt Pt + Re, Sb2O3(s), Sb2O4(s)parallel to O(-2)parallel to air, Pt Pt + Re, Sb2O3(s), Sb2O4(s), Te(1)parallel to O(-2)parallel to air, Pt the equilibrium oxygen potential in the pseudobinary Te-TeO2, Sb2O3-Sb2O4 and in the Sb2O3-Sb2O4-Te pseudoternary systems was determined in the temperature range 700-1173 K. In addition, the pseudobinary sections Sb2O3-Te, Sb2O3-Sb2O4 (1:1)-Te and Sb2O4-Te were examined by DTA in the temperature range 500-1300 K. Using these results the evolution of the pseudoternary system with temperature can be suggested. It was found that, at 718 K, a ternary eutectic with a composition close to pure Te appears in the system. At a higher temperature, 920 K, another liquid phase is formed, which is characteristic of the ternary four-phase equilibrium L(2) + Sb2O4(s)+ Sb2O3(s) = L(1).