The effects of Cr-and S-impurities on the cathode performances were examined at the mixed ionic-electronic conducting La0.6Sr 0.4Co0.2Fe0.8O3 (LSCF) cathode. Under exposures to CrO3 and SO2, the cathode performance decreased drastically by forming SrCrO4 and SrSO4 at the LSCF grain surfaces and electrochemical active sites. The main degradation factors of LSCF cathode was the decrease of surface reaction rates by the impurities. The Sr-diffusion and depletion in the LSCF structures can affect the cathode performance degradation. Relatively large amounts of Sr were depleted in the LSCF grains under CrO3 exposures by forming a thick SrCrO 4 at the Pt-mesh/LSCF cathode interfaces, while small amounts of Sr-depletion in the LSCF grains under SO2 exposures.