Copper-modified ceria catalysts, (CuO)_x/Ce_0.9Cu_0.1O₂ nanospheres, for low-temperature CO oxidation were fabricated simply by using the hydrothermal synthesis of Cu-doped CeO₂ (Ce_0.9Cu_0.1O₂) nanospheres followed by deposition of CuO over Ce_0.9Cu_0.1O₂. The X-ray diffraction and electron spectroscopy characterizations demonstrated that the as-prepared nanospheres were composed of cubic CeO₂ and monoclinic CuO with a typical diameter of around 70 nm. Moreover, the X-ray photoelectron spectroscopy (XPS) analysis illustrated the coexistence of Ce⁴⁺/Ce³⁺ and Cu²⁺/Cu⁺ redox couples in (CuO)_x/Ce_0.9Cu_0.1O₂ and H₂ temperature-programmed reduction (TPR) measurements indicated the excellent reduction behavior of the catalyst. The Raman spectra illustrated the oxygen vacancy in (CuO)_0.3/Ce_0.9Cu_0.1O₂, and diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) demonstrated the stable existence of Cu⁺ species during CO oxidation. The (CuO)_x/Ce_0.9Cu_0.1O₂ nanospheres showed excellent catalytic activity toward CO oxidation in normal feed gas (volume ratio of CO/O₂/N₂=1:10:89) at ambient temperature. Catalytic tests revealed that the proportion of CuO in the final product has a strong influence on the resultant catalytic activities. The (CuO)_x/Ce_0.9Cu_0.1O₂ nanospheres hold great application potential as new catalysts for CO oxidation.