We have investigated the oxidation behavior of epi- Si0.7Ge0.3 films in dry oxygen ambient. Epi- Si0.7Ge0.3 films about 500Angstrom in thickness were deposited on (100) Si wafers by UHV-CVD system. Oxidation was carried out in a conventional tube furnace at 800degreesC. In this study, it was found that Ge piles up at the oxide/substrate interface, forming a Ge-rich layer. Because of the large difference in the heat of formation between SiO2 (-730.4KJ/mol at 1000K) and GeO2 (-387.07 at 1000K) [1], the Si is to be more reactive than Ge to oxygen. The oxidation rate of SiGe in a dry oxygen environment is found to be essentially the same as that of pure Si.