The air-exposed surfaces of sintered UC samples at room temperature were examined by X-ray photoelectron spectroscopy (XPS). Elemental depth profiles reveal that the surface of UC consists of a top layer of small amounts of UO2+ ; this very thin layer is x followed by a layer containing uranium dioxide, uranium monocarbide and free carbon and then bulk UC. The binding energy of U4f7/2 and C1s peaks of UC is found to be 378.2 eV and 282 eV, respectively. Quantitative analysis indicates that the C/U atomic ratio of clean UC surfaces is approximately 1?1, which is consistent with stoichiometric UC, but there exists small amounts of dissolved oxygen on sputter-cleaned UC surfaces. The oxidation mechanism of UC has been also discussed.