Nanostructured CeO2-x and Cu0.15Ce0.85O2-x were synthesized by high-pressure magnetron sputtering. X-ray diffraction was used for phase analysis and grain size characterization. The structural analysis indicated that Cu was highly dispersed, which could be explained by surface segregation on cerium oxide nanocrystals. The reduction and oxidation of dispersed copper in nanostructured Cu0.15Ce0.85O2-x was investigated by isothermal gravimetric analysis (IGA) and X-ray photoelectron spectroscopy (XPS). In IGA, the sample weight was measured at constant temperature during in situ reduction and oxidation in 2% CO/He or 5% H-2/He and 15% O-2/He, respectively. The weight changes of microcrystalline CeO2 and nanocrystalline CeO2-x, and Cu0.15Ce0.85O2-x samples were measured at temperatures between 200 and 500 degrees C. The analysis revealed that more than one oxygen atom was extracted per Cu atom in Cu0.15Ce0.85O2-x during reduction, which was reversibly restored during oxidation. The Cu valence state in Cu0.15Ce0.85O2-x after oxidation or reduction was independently determined by XPS. The Cu 2p core-level spectra and LMM Auger spectra of Cu0.15Ce0.85O2-x were compared with those of a polycrystalline copper reference. The analysis showed that all three oxidation stares of copper (i.e., 0, 1+ and 2+) could be present depending on the reduction/oxidation specifications. Furthermore, Cu-0 and Cu1+ were found to coexist in a stable state under certain conditions.