In fourth-generation lead–bismuth eutectic (LBE) fast reactors, controlling the dissolved oxygen concentration in LBE is critical for mitigating corrosion of structural materials, making accurate measurement of oxygen concentration essential. The oxygen sensors, based on the Nernst principle, rely on the high ionic conductivity and low electronic conductivity of solid electrolytes, which are assembled into electrochemical cells for oxygen concentration measurement. Oxygen sensors with metal–metal oxide reference electrodes (including Cu/Cu2O and Ni/NiO) were tested in the LBE eutectic under saturated oxygen conditions, within a temperature range of 200–450 °C, to assess the performance of the oxygen sensors at low temperatures. Different solid electrolyte materials (5-YSZ and 8-YSZ) and measurement setups were employed to compare the performance of these reference electrodes against those with air/La0.8Sr0.2Co0.8Fe0.2O3 (LSCF) reference electrodes. The results indicate that oxygen sensors using 8-YSZ as the solid electrolyte outperformed those with 5-YSZ. The oxygen sensor with a Cu/Cu2O reference electrode proved suitable for measuring oxygen concentrations within the 200–450 °C temperature range, providing stable signals and response speeds comparable to those of air/LSCF electrode-based sensors. However, the sensor with a Ni/NiO reference electrode showed significant deviation from expected values below 300 °C.