The degradation of La 0.6Sr 0.4Co 0.2Fe 0.8O 3 (LSCF) cathode performance were investigated under relatively high pressures of impurities with Cr and S. AC impedance and DC currents were measured as a function of operation time. The cathode polarization rapidly increased when exposure to CrO 3 and SO 2 due to active sites vanishing with impurities. The distributions of Cr and S in the porous LSCF were different due to the chemical reactivity and electrochemical effects. A significant amount of SrCrO 4 was deposited at the gas inlet of cathode surface region whereas small spots of SrSO 4 were distributed inside the porous LSCF cathode. From the trends of polarization increase, the decrease trends and life time of cathodes were estimated for the availability of cathodes.