In the present study we demonstrate that the activity and selectivity of SnO2 nanocatalysts during the aqueous-phase electrochemical reduction CO2 can be effectively tailored by coupling of nanostructured CuO to form SnO2-CuO nanocomposites. Comparing the Faradaic selectivity of formate as a function of the applied electrode potential and electrolysis time, it is found that CuO incorporation can significantly improve the activity of SnO2-CuO composite catalysts. When the ratio of CuO in the bulk composite was 50%, the formed SnO2(50%)-CuO( 50%) nanocomposite gives the best catalytic performance with the onset potential as early as -0.75 V and the current density at -1.25 V as high as about-24 mA cm(-2). Ion chromatography measurement demonstrates that when the electrolysis was held at -1.0 V for 1 h in 0.5M KHCO3, the maximum Faradaic efficiency of formate production can be high up to 74.1%. The outstanding stability of SnO2 nanocatalyst fabricated electrode is also evidenced due to the stronger synergistic effect induced by CuO compositing, where the SnO2(50%)-CuO (50%) composite catalyst keeps a steady current density without any dropt over 30 h' continuous electrolysis approach. The improved performances are deduced from the strong synergistic interactions between SnO2 and CuO nanocomposite as evidenced from SEM, XRD and XPS analysis results.