When we use NiO based particle as an oxygen carrier in a chemical looping combustion system, the fuel conversion and the CO2 selectivity decreased with increasing reaction temperature within high temperature range (>900 ℃) due to the increment of exhaust CO concentration from reduction reactor. To improve reduction reactivity at high temperature, the applicable metal oxide component was selected by calculation of the equilibrium CO concentration of metal oxide components. After that, feasibility of reduction reactivity improvement at high temperature was checked by using solid mixture of the selected metal oxide particle and NiO based oxygen carrier. The reactivity was measured and investigated using batch type fluidized bed. The solid mixture of Co3O4/CoAl2O4(10%) and OCN706-1100(90%) showed higher fuel conversion, higher CO2 selectivity and lower CO concentration than OCN706-1100 (100%) cases. Consequently, we could conclude that improvement of reduction reactivity at high temperature range by adding some Co3O4 based oxygen carrier was feasible.