Thermodynamic predictions and electrochemical analysis of secondary phase formation in SO2 containing atmosphere on the surface of La1-xSrxCo0.2Fe0.8O3 +/-delta (x = 0.2-0.4) electrodes of solid oxide fuel cells have been carried out utilizing the CALculation of Phase Diagram (CALPHAD) approach. Impacts of temperature, SO2 partial pressure, O-2 partial pressure as well as the cathode composition on the formation of secondary phases have been investigated and correlated with the previous investigations in the literature. The results predict that SrSO4, CoFe2O4, La2O2SO4, and La-2(SO4)(3) has the possibility to form on the surface and at the cathode/electrolyte interface as a result of SO2 existence in the system. It is also investigated that degradation occurs more severe for La0.6Sr0.4Co0.2Fe0.8O3 +/-delta LSCF-7328 and LSCF-8228, due to the formation of a higher amount of secondary phases, specifically SrSO4. The results demonstrate the effectiveness of the computational thermodynamic modeling in the prediction of interaction and performance stability of SOFC cathodes in the presence of contaminants. Crown Copyright (C) 2018 Published by Elsevier Ltd. All rights reserved.