A series of CoxMn1-xOy catalysts were prepared via the co-precipitation method by varying the cobalt content, and were applied to selective CO oxidation in the presence of H-2, CO2, and H2O. The prepared catalysts were characterized by means of N-2 physisorption, X-ray diffraction, temperature-programmed reduction, and temperature-programmed desorption of oxygen. Among the evaluated catalysts, the highest catalytic activity was achieved with the formulation Co0.8Mn0.2Oy. The surface area of the Co0.8Mn0.2Oy catalyst could be maximized by utilizing a lower feeding rate of the precipitant solution and calcination temperature in the preparation process. The catalytic reducibility and the amount of active oxygen were enhanced by increasing the Co content of the Co-Mn-O catalyst only except for Co1.0Mn0.0Oy catalyst. The catalytic activity was effectively enhanced by increasing the catalyst surface area, which is proportional to the amount of active surface oxygen.