Copper manganese oxides (CMOs) were synthesized using a co-precipitation method with different precursors and precipitants for carbon monoxide oxidation. The as-synthesized catalysts were characterized by powder X-ray diffraction (XRD), low temperature N-2 sorption, Fourier transform-infrared spectroscopy (FT-IR), H-2-temperature programmed reduction (H-2-TPR), and thermal gravimetric analysis (TGA). Their catalytic activities for CO oxidation were tested by temperature programmed reaction. The results showed that the activity of CO oxidation strongly depended on the combination of precipitant and precursor anions, ranking in the order (Ac- + CO32-) > (NO3- + CO32-) > (Ac- + OH-) > (NO3- + OH-). The crystalline phase of copper manganese oxides obtained using strong electrolyte (OH-) as the precipitant were mainly spinel Cu1.5Mn1.5O4, while the catalysts prepared with weak electrolyte (CO32-) as the precipitant mostly comprised of MnCO3, Mn2O3 and CuO, and showed a much higher CO oxidation activity than that of the Cu1.5Mn1.5O4. Keeping the same precipitant while changing the precursor caused a change in the H-2 consumption which influenced the CO oxidation activity. A suitable combination of precipitant and precursor resulted in the most efficient CO oxidation catalyst. (c) 2012 Elsevier B.V. All rights reserved.