A new and easy method is developed to determine the oxygen non-stoichiometry of perovskite materials under equilibrium conditions. The method is based on the complete decomposition of the powder to stoichiometric metal oxides and/or metal carbonates by using CO2 as reacting gas. The oxygen non-stoichiometry is calculated from the mass change caused by this reaction. Its applicability is demonstrated by using SrCoO3-delta. BaCoO3-delta, BaFeO3-delta and BaCeO3-delta as representative materials. The oxygen non-stoichiometry (delta) values at 950 degrees C in air were determined as 0.48, 036, 0.43 and 0.03 respectively. These values can be used as reference points for oxygen non-stoichiometry analysis at other temperatures. (C) 2012 Elsevier B.V. All rights reserved.