Thermodynamics of defects in the (LaxCa1-x)FeO3-delta perovskite is modeled by means of the CALPHAD approach. In this phase, the A-sites are occupied by La+3 and Ca+2, and Fe in the B-site is known to exist in +2, +3, and +4 oxidation states depending on the oxygen vacancy concentration. Therefore, the ionic sublattice model: (La+3, Ca+2)(Fe+2, Fe+3, Fe+4)(O-2, Va)(3) is used to describe the phase, and the model parameters are evaluated from experimental oxygen nonstoichiometry and phase equilibria data. With the Fe+2 and Fe+4 treated as the major species in the B-site, the calculated phase diagrams are in good agreement with the experimentally reported phase equilibria data. The concentration of various defects in (LaxCa1-x)FeO3-delta as a function of oxygen partial pressure and temperature are calculated at different concentrations of Ca. At high oxygen partial pressures, Fe+4 is predicted to be dominant while Fe+2 is dominant at low oxygen partial pressures. (C) 2013 The Electrochemical Society. All rights reserved.