The effect of support reducibility and reduction treatment was studied in SiO2 nanospheres and CeO2 nanorods supported CuOx (0 <= x <= 1) catalysts on CO oxidation. CuO nanoparticles were impregnated on SiO2 nanospheres and CeO2 nanorods using thermal decomposition method and then the samples were oxidized in air at different temperatures (400-600 degrees C). The sample oxidized at 400 degrees C was also further reduced under hydrogen atmosphere to compare the effect of reduction treatment on the catalytic activity. Detailed XRD, Raman, H-2-TPR, and CO oxidation analyses were carried out to understand the effect of CuOx-support interaction and different CuOx species on the catalytic performance. Compared to SiO2 nanospheres supported CuOx catalysts, both CuO/CeO2 and reduced CuOx/CeO2 catalysts exhibited superior catalytic performance in terms of CO conversion and low-temperature hydrogen consumption. The enhanced activity of CeO2 nanorods supported CuOx catalysts was correlated strongly to the surface defects on CeO2 nanorods and interfacial structures. (C) 2017 Elsevier B.V. All rights reserved.