Formic acid (HCOOH) is a highlyenergy-efficient productof electrochemical CO2 reduction reaction (CO2RR).Bismuth-based catalysts have shown promise in the conversion ofCO2 to formic acid, but there is still agreat need for further improvement inselectivity and activity. Herein, we report the preparation of Bi nanosheets decorated by cerium oxide nanoparticles (CeOx) with high Ce3+/Ce4+ ratio and rich oxygen vacancies. The CeOx nanoparticles affect on the electronic structures of bismuth, enhance the CO2 adsorption, and thus promote the CO2RR properties of Bi nanosheets. Compared with elemental Bi nanosheets, the hetero-structured CeOx/Bi nanosheets exhibit much higher activity overa wide potential window, showing a current density of 16.1 mA cm-2 with a Faradaic efficiency of 91.1% at -0.9 V vs. reversible hydrogen electrode.