In conventional solid oxide electrolysis mode, most of the electric power is consumed to overcome the high chemical potential in forcing the oxygen to diffuse through the electrolyte. In this paper, a novel methane-assisted H₂O/CO₂ co-electrolyzer was designed by combining solid oxide electrolysis cell (SOEC) with partial oxidation of methane (POM) to generate syngas in both sides. In POM-SOEC mode, methane is fed to the oxygen electrode to react with the oxygen produced by the electrolysis process, thus to reduce the chemical potential. Experiment performed on the Ni-YSZ/YSZ/SFM-YSZ single cell showed a voltage reduction from 1.2 V to 0.2 V compared to the conventional electrolysis mode at the same current density. The constant current test indicated that no obvious degradation was detected in 50 h operation.