The electroreduction of carbon dioxide (CO2) into fuels and other chemicals is an exciting approach to address the urgent climate and energy challenges. However, the unsatisfied efficiency and selectivity for CO2 reduction reaction (CO2RR) with conventional electrocatalysts are the major obstacles. Herein, a facile and effective method is developed to deposit ultrasmall SnO2 nanocrystals on nitrogen-doped graphene via in-situ conversion strategies for highly efficient CO2RR. The comparison studies reveal that the electrocatalytic activity of such electrocatalysts relies on the loading of SnO2 on graphene and the nitrogen doping. The optimal electrocatalyst exhibits a high selectivity for CO2 electroreduction to formate and carbon monoxide at low overpotential similar to 0.6 V) with a faradaic efficiency of similar to 89% and a current density of similar to 21.3 mA/cm(2). Additionally, the optimal electrocatalyst shows an excellent stability for 20 h. The good performance would be contributed to the ensemble effect between the highly dispersed ultrasmall SnO2 nanocrystals and the nitrogen doping on graphene sheets. This work thus provides a rational design strategy for developing efficient CO2 reduction catalysts.