The surface chemistry of perovskite-type lanthanum transition metal oxides is an important parameter in high-temperature electrochemical devices such as solid oxide fuel cells (SOFCs). Strontium segregation on the surface of lanthanum strontium cobalt oxides (LSC) may lead to poor oxygen reduction kinetics. However, previous studies have not sufficiently addressed the oxide surface chemistry, including the oxidation change of LSC under cathodic polarization. In this study, operando total-reflection X-ray fluorescence absorption and X-ray fluorescence spectroscopy were performed to investigate cathodic polarization at high temperature (773 K) and at 1 atm pressure. Dense thin-film electrodes of La Sr CoO (LSC ) on Zr Y O electrolytes with a gadolinium-doped ceria interlayer were examined as model SOFC cathodes. This may be the first time that predominant surface reduction of cobalt is directly observed by using LSC under cathodic polarization. This phenomenon is related to strontium enrichment on the LSC surface. (La Sr ) CoO decoration on LSC enhanced the oxygen reduction kinetics compared with that of bare LSC . This is due to the suppression of cobalt surface reduction and Sr enrichment in the LSC phase. 0.6 0.4 3 113 0.92 0.08 1.96 113 0.5 0.5 2 4 113 113 113