The oxidation behavior of chemical vapor infiltration (CVI), molten silicon infiltration (MSI) and CVI+MSI C/SiC composites at 500-1 400 ℃ was studied. The oxidation below 900 ℃ increased successively for CVI, CVI+MSI and MSI composites. However, the oxidation of CVI composite above 1 000 ℃ was much faster than that of MSI and CVI+MSI composites. As active carbon atoms produced by siliconization of fibers during MSI process were oxidized first and decreased initial oxidation temperature. The initial oxidation temperature of MSI, MSI+CVI and CVI composites was 526, 552 and 710 ℃, respectively. New active carbon atoms were generated due to the breaking of 2D molecular chains during oxidation, so the activation energy of three C/SiC composites was decreased gradually at 500-800 ℃ with oxidation process, exhibiting a self-catalytic characteristic.