To avoid urban air pollution, the development of SO2 sensor with suitable detection range applied for coal-fired boiler flue gas treatment system is of vital importance due to SO2’s extremely toxic and harmful nature. In this work, we developed different molar ratio Mn/Ce composite oxides as sensing electrode material of YSZ-based mixed potential type SO2 sensors. When Mn2+: Ce3+ = 6: 10(in molar ratio), the sensor had the highest response ( − 30 mV to 10 ppm SO2) due to sensing electrode material’s superior electrochemical catalytic ac tivity, which was confirmed by polarization curves. During the test, SO2 converted to sulfate depositing on electrode surface, which was proved by XPS, and therefore the upper detection limit was brought down. MnSO4 was added to sensing electrode material in varying amount and cyclic voltammetry (CV) curves of the sensors were tested in 10 ppm SO2 at 650 ◦C to investigate changes in electrochemical characteristics. The change of sulfate content in sensing electrode material could control the equilibrium state of electrochemical reaction and its progress, thus influencing the detection range. In addition, selectivity, stability under different oxygen con centration and humidity, long-term stability of the SO2 sensor were studied in detail.