Abstract: Cerium metal is considered as a surrogate of plutonium because of their similarities in physical and chemical properties for scientific research. In order to investigate the feasibility of cerium as a surrogate of plutonium under ultra-high vacuum condition (UHV), stabilities of surface oxides on cerium metal under UHV conditions were studied by the X-ray photoelectron spectroscopy (XPS). Cerium sample was stored in analysis chamber under UHV condition at room temperature for 19 d and 3 d, respectively. And then, the sample was heated to 673 K and 873 K in order to see any changes on the surface. The results show that the stabilities of surface oxides on cerium metal vary with temperature. At room temperature, there is no change observable on the surface from Ce3d XPS spectra after the storage of 19 d and 3 d respectively. And some deoxidization is found at 673 K and 873 K under UHV condition. Surface oxides on cerium sample transform from CeO₂ to Ce₂O₃. The transformation is similar to that of plutonium, but the reacting condition for cerium is more rigid than that for plutonium. Attempts on deducing the process of deoxidization was carried out by thermodynamical calculations, and the mechanism may not be the same. So there are some difference in properties under UHV between surface oxides on cerium metal and those on plutonium. 