Perovskite type oxides based on alkaline-earth and/or rare-earth containing cobaltites with high electronic and ionic conductivities are suitable for cathodes for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Much of the prior work, in particular, has been focused on Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) because of their high catalytic activity and a sufficiently high electronic conductivity. This study focuses on the redox behavior and stability of BSCF and LSCF at low oxygen partial pressures. The variation of oxygen non-stoichiometry (delta) and its effect on the electrical conductivity of the BSCF and LSCF are investigated using coulometric titration in a wide range of oxygen partial pressure. Thermodynamic properties including oxidation enthalpies and entropies are determined from the oxidation isotherms. The BSCF and LSCF are considered to be a suitable cathode material of IT-SOFC in terms of electrical conductivity and redox stability. (C) 2012 Elsevier Ltd. All rights reserved.