Chemical looping air separation (CLAS) is considered as a novel process for the economic production of oxygen in the advanced clean coal technologies, such as oxy-fuel combustion and integrated gasification combined cycles (IGCC). In the CLAS process, oxygen is separated from air via the cyclic redox reactions of oxygen carriers, i.e., the oxidation in air and the reduction under the inert gases, such as steam and/or CO2. The performance of the oxygen carrier, therefore, plays a crucial role in determining the feasibility of the CLAS process and its operating costs. The present study is aiming for the development of an impregnated Cu Mg-based oxygen carrier with SiO2 as a support for CLAS, with a particular focus on improving the long-term stability of the CuO/SiO2 carrier. The reactivity of Cu-Mg-SiO2 oxygen carriers was evaluated using thermogravimetric analysis (TGA) at the temperatures between 850 and 950 C in air and N-2 environments for the oxidation and reduction, respectively. The results indicated that all Cu Mg-based oxygen carriers appear to have better stability compared to the CuO/SiO2 monometallic oxygen carriers. Generally, it was observed that the oxygen carriers with a higher MgO content had a higher reactivity, in particular, for the reduction process. The Cu Mg-based oxygen carriers with an optimum weight ratio of MgO/CuO, viz., no less than 1:2, exhibited the most stable performance among all of the studied carriers for 41 redox cycles test.