Spectroscopic ellipsometry has been used to investigate, for the first time, the optical properties of oxide films on SiC to discuss the difference of the structures of SiC/SiO2 interfaces with oxidation processes, thermal oxidation in dry oxygen, pyrogenic oxidation and low temperature deposition of oxides by chemical vapor deposition. It was found that there exist interface layers with high refractive indices between SiC and SiO2, the values of which are larger than those of SiC and SiO2 and depend on the oxidation process. The validity of the evaluation of refractive indices of the interfaces has also been discussed.