Carbon fiber reinforced carbon matrix composites, C/Cs, process excellent high temperature capability, but have the deficit of weakness against high temperature oxidation. Thus, C/Cs are generally used with an anti-oxidation coating, for which silicon carbide, SiC, is frequently used. However, the SiC coating is slowly but gradually oxidized. The purpose of the present study is to develop a sensor, which can detect oxidation rates at severe high temperature environments. The sensor under discussion is composed of SiC/C multi-layered coating formed on a substrate and can measure the electric resistance of the multi-layered coating. In this paper, it is shown that this sensor has capability of in-situ monitoring of oxidation rates of SiC coating up to temperatures of 1800K.