Influence of calcination temperature (400−800°C) on the structure and catalytic activity of CuO x -CoO y -CeO 2 ternary mixed oxide (atomic Cu:Co:Ce ratio of 1:5:5) prepared by co-precipitation method is investigated by N 2 physisorption, XRD, TPR, TEM, TG-DTA, XPS, and CO oxidation reaction. The as-synthesized CuO x -CoO y -CeO 2 undergoes successive structural changes with the calcination temperature, involving the hydroxide dehydration below 400°C, enhanced interaction between Co 3 O 4 and CeO 2 at ca. 600°C, and Co 3 O 4 decomposition to CoO at 700°C. The catalyst calcined at 600°C shows a relative enrichment of Cu + on the surface of CuO x -CoO y -CeO 2 and an enhanced interaction between Co 3 O 4 and CeO 2 along with the appearance of oxygen vacancies in CeO 2 , which seems to be responsible for its highest catalytic activity for CO oxidation among all the tested catalysts. The complete conversion of CO is obtained at 70°C and about 50% of CO conversion is reached at 55°C.