Tin oxide nanoparticles (SnO 2 NPs) as electrocatalyst for the production of formate from CO 2 reduction reaction (CO 2 RR). We synthesize, characterize and evaluate high surface area SnO 2 NPs (2.4 nm and 299 m 2 g-1 in diameter size and surface area, respectively), for the continuous production of formate at high current density within a flow electrolyzer. SnO 2 NPs under Ar and CO 2 reduction conditions were studied by cyclic voltammetry. SnO 2based gas diffusion electrodes (SnO 2-GDEs) were manufactured to perform continuous CO 2 RR. A maximum formate concentration value of 27 g L-1 was achieved with a Faradaic efficiency (FE) of 44.9% at 300 mA cm-2 , which was significantly stable and reproducible when operated up to 10 h. Nevertheless, ohmic drop contribution due to the semiconducting properties of SnO 2 was not negligible. The low total FE (< 60%) of products pointed out a leakage of formate by crossover migration through the membrane from the catholyte towards the anolyte.