Performance degradation of SOFC cathodes has been partly attributed to sulfur dioxide (SO2), which is one of the major impurities naturally present in air. In this work, the sulfur poisoning behavior of (LaSr)(CoFe)O-3 (LSCF) cathodes exposed to 1 ppm of SO2 in air was investigated as a function of time under various operation temperatures of 923 K, 973 K, and 1073 K. Severe performance degradation was observed at low temperatures of 923 K and 973 K. For these cases, only the polarization resistance (Rp) was increased, additionally no sulfur component was detected in the LSCF cathode. At 1073 K, both R-p and ohmic resistance (R-ohmic) increased during the progress of degradation and SrSO4 was observed in cathode, especially near the LSCF/GDC interface. Plausible sulfur poisoning mechanisms were proposed based on the observed experimental phenomena. (C) 2016 The Electrochemical Society. All rights reserved.