Abstract : Abstract YBaCo4O7 ± δ was found to be thermodynamically stable in air at T > 900 °C whereas its thermodynamic stability at 950 °C is limited by the range of oxygen partial pressures - 5.05 ≤ log(pO2/atm) ≤ - 0.5. Oxygen content in YBaCo4O7 ± δ at 950 °C slightly decreases from 7.009 at log(pO2/atm) = - 0.5 to 6.953 in the atmosphere with log(pO2/atm) = - 5.05. YBaCo4O7 ± δ decomposes into the mixture of YCoO3-δ, BaCoO3-δ and Co3O4 at 950 °C in atmosphere with log(pO2/atm) > - 0.5 whereas in atmosphere with log(pO2/atm) < - 5.05 Y2BaCoO5, BaCoO2 and CoO were identified as the products of YBaCo4O7 ± δ decomposition. © 2015 Elsevier B.V.