The effect of CuPt nanoclusters on TiO2 on the production of CH4 was investigated. Cu provides active sites for CO2 reduction, and Pt enhances the production of CH4 by promoting the protonation of CO, which is intermediate of CO2. In addition, the small size of the alloy gives rise to higher CH4 production because the CuPt nanoclusters have low coordination number. XPS analysis reveals that hydroxyl group on the surface of TiO2 facilitates CO2 reduction. The CO2- on the CuPt nanoclusters might react with TiOH and form COOH as an intermediate. The reuslt implies that the co-adsorption of CO2 onto the CuPt bimetallic nanoclusters and TiO2 can enhance the efficiency of CO2 reduction.