In this work, the morphology controlled SnO2 nanosphere catalyst has been successfully synthesized and applied to electrochemical CO2 reduction to formic acid in 0.5 M KHCO3. The catalysts were synthesized by a simple hydrothermal method under controlling the different proportions of ethanol to distilled water as mixed solvent. The obtained catalysts were then coated on gas diffusion electrode (SnO2/GDE) as working electrode. It was found that the catalyst prepared from 50% content of ethanol gives the best catalytic activity towards CO2 reduction, where the onset potential was found to be 300 mV more anodic than that of hydrogen evolution. Meanwhile, the SnO2/GDE-50 showed the most stable property for CO2 reduction. The current density and faradaic efficiency increased as the potential increased, reaching a maximum at -1.7 V vs. SHE. At this stage, the maximum faradaic efficiency of 68% with a current density of 6 mA cm-2 was obtained. Moreover, the production rate of format exhibits a maximum value of 518.2 mg L-1 at the cathode potential of -1.9 V vs. SHE.