SnO2-based materials are promising catalysts for CO2 electrochemical reduction due to their attractive selectivity for C1 products (formate and carbon monoxide) but they tend to suffer high overpotential and poor stability. Here, a porous SnO2/ZnO catalyst is synthesized via hydroxides coprecipitation, hydrothermal treatment, and carbon black template calcination. SnO2 nanocrystals are produced by calcination of tin hydroxides while the growth of ZnO nanocrystals is associated with carbon black template. The porous SnO2/ZnO catalyst presents a stable Faradaic efficiency of >90% for CO2 reduction at an applied voltage of −0.7 V versus reversible hydrogen electrode and a C1 current density of 9.53 mA/cm2 over a testing period of 100 h. The improved performance is originated from abundant hetero-junctions and lattice defects of SnO2 and ZnO nanocrystals, large specific surface area, and grain boundary. This study provides a facile method to fabricate porous and nanocrystal metal oxides electrocatalysts for electrochemical processes.