Among several issues in the degradation of the cathode performance of solid oxide fuel cells (SOFC), sulfur poisoning is one of the most studied so far. Several experiments on the cell performance have been performed to understand the poisoning mechanism on SOFC cathodes. In this study, the performance of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) porous cathode on Ce_0.9Gd_0.1O_1.95 (GDC) electrolyte was evaluated at 0.01 ppm SO₂ gas. The evaluation was carried out at various temperatures as function of temperature and poisoning time under -0.3 A of dc bias. The 0.01 ppm SO₂ gas was feed into the measurement chamber after stable condition was achieved during I-V test. A large degradation was observed at low operation temperature (823 K). In contrast at high operation temperature (1023 K) degradation was hardly observed. These results are in good agreement with the evaluation of the surface oxygen exchange coefficient, k*, by Adler – Lane – Steele model. The k* which was determined for the sample operated at low operation temperature showed larger degradation over poisoning time compared to that at high temperature. This indicates that the surface of LSCF was largely affected by sulfur poisoning. The evaluation of poisoning mechanism and compositional change of LSCF cathode during sulfur poisoning will be discussed in this presentation.