The importance of tin oxide (SnOx) to the efficiency of CO2 reduction on Sn was evaluated by comparing the activity of Sn electrodes that had been subjected to different pre-electrolysis treatments. In aqueous NaHCO3 solution saturated with CO2, a Sn electrode with a native SnOx layer exhibited potential-dependent CO2 reduction activity consistent with previously reported activity. In contrast, an electrode etched to expose fresh Sn-0 surface exhibited higher overall current densities but almost exclusive H-2 evolution over the entire 0.5 V range of potentials examined. Subsequently, a thin-film catalyst was prepared by simultaneous electrodeposition of Sn-0 and SnOx on a Ti electrode. This catalyst exhibited up to 8-fold higher partial current density and 4-fold higher faradaic efficiency for CO2 reduction than a Sn electrode with a native SnOx layer. Our results implicate the participation of SnOx in the CO2 reduction pathway on Sn electrodes and suggest that metal/metal oxide composite materials are promising catalysts for sustainable fuel synthesis.