Polarization modulated infrared reflection absorption spectroscopy (PM-IRRAS), which is one of the advanced FT-IR methods, was combined with conventional electrochemical techniques for in situ observation of high temperature electrode reactions at 773 K in oxygen partial pressure of 3 × 104 Pa. PM-IRRAS method can detect surface species selectively with high sensitivity at high temperatures without background measurement to cancel the infrared absorption by gas phase. Two different O2(g), Pt/YSZ electrochemical half cells were prepared as simple models of gas-electrodes. One of them had a working electrode which was composed of uniformly distributed platinum; the other had an island-networked platinum electrode. On the former electrode, PM-IRRAS detected a concentration change of adsorbed oxygen on Pt electrode with controlled cathodic overpotential. On the other hand, for the latter sample that showed smaller cathodic current, the signal of the adsorbed oxygen was suppressed by SiO2 impurity, whose spectrum was detected at 1220 cm- 1 by PM-IRRAS. It was shown that PM-IRRAS gives useful information on the state of adsorbed species which affect the electrode kinetics and the cell performance.