A series of Co-Cu composite oxides with different Co/Cu atomic ratios were prepared by a co-precipitation method. XRD, N-2 sorption, TEM, XPS, H-2-TPR, CO-TPR, CO-TPD and O-2-TPD were used to characterize the structure and redox properties of the composite oxides. Only spinel structure of Co3O4 phase was confirmed for the Co-Cu composite oxides with Co/Cu ratios of 4/1 and 2/1, but the particle sizes of these composite oxides decreased evidently compared with Co3O4. These composite oxides could be reduced at lower temperatures than Co3O4 by either H-2 or CO. CO and O-2 adsorption amounts over the composite oxides were significantly higher than those over Co3O4. These results indicated a strong interaction between cobalt and copper species in the composite samples, possibly suggesting the formation of Cu (x) Co3-x O-4 solid solution. For the preferential oxidation of CO in a H-2-rich stream, the Co-Cu composite oxides (Co/Cu = 4/1-1/1) showed distinctly higher catalytic activities than both Co3O4 and CuO, and the formation of Cu (x) Co3-x O-4 solid solution was proposed to contribute to the high catalytic activity of the composite catalysts. The Co-Cu composite oxide was found to exhibit higher catalytic activity than several other Co3O4-based binary oxides including Co-Ce, Co-Ni, Co-Fe and Co-Zn oxides.