Oxidation behavior of high-purity Si-SiC composite (molar ratio 40/60) was studied during reactions at 1600K for 15h in Ar-O2 (PO2: 0.02-97kPa) atmospheres to evaluate the oxidation-resistant property. The oxidation rate was determined by measuring CO and CO2 concentrations during the oxidation using a quadrupole mass spectrometer. The oxidation kinetics obeyed the linear-parabolic law at high oxygen partial pressures (97kPa) and obeyed the linear law at low oxygen partial pressures (0.02kPa). The former case accompanied the weight gain, while the latter the weight loss. The oxygen partial pressure causing the transition from passive to active oxidation was estimated to lie between 0.1kPa and 0.02kPa. In passive oxidation, apparent low oxidizability of Si as compared with that of SiC was considered to result from the conversion of Si in the surface layer of the sample into SiC caused by its reaction with C released from SiC. Cooperative actions between Si and SiC were discussed in connection with the oxidation resistance of Si-SiC composite.