Thin films of uranium cerium mixed oxides UxCe1-xO2 +/- y have been prepared by DC sputtering and characterized by X-ray photoelectron spectroscopy (XPS). Reduction and oxidation properties were analysed by exposing the films to atomic hydrogen and to atomic oxygen, respectively. Possible interaction between uranium and cerium were investigated by comparing the compounds to the single oxides of cerium and uranium. Uranium seems to promote the reduction of cerium. Conversely cerium promotes oxidation of uranium. Under our deposition conditions, it was not possible to produce pure U(IV) together with pure Ce(IV). The synthesis of U2O5 with U(V) cannot be obtained directly by DC sputtering, whereas with addition of cerium, U(V) seems to be stabilized and obtained more easily. This can be related to a charge transfer between Ce(IV) and U(IV).