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 Co(3)O(4) 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 Co(3)O(4). These composite oxides could be reduced at lower temperatures than Co(3)O(4) by either H(2) or CO. CO and O(2) adsorption amounts over the composite oxides were significantly higher than those over Co(3)O(4). These results indicated a strong interaction between cobalt and copper species in the composite samples, possibly suggesting the formation of Cu (x) Co(3-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 Co(3)O(4) and CuO, and the formation of Cu (x) Co(3-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 Co(3)O(4)-based binary oxides including Co-Ce, Co-Ni, Co-Fe and Co-Zn oxides. ; National Natural Science Foundation of China [20773099]; National Basic Research Program of China [2005CB221408]; Key Scientific Project of Fujian Province of China [2005HZ01-3]; Program for New Century Excellent Talents in Fujian province