This paper deals with solid state electrolyte type gas sensors based on mixed potential mechanism using yttria stabilized zirconia (YSZ) as solid electrolyte and MTiO₃(M: Zn, Co and Ni) as sensing electrodes (SEs) for monitoring very low concentrations of SO₂in atmospheric environments. Among all the devices attached with different SEs, ZnTiO₃-SE brought about the highest response value of −22.5 mV to 1 ppm SO₂at 600℃and even down to 100 ppb SO₂with the response value of −2.5 mV. Meanwhile, the measured ΔV of the sensor was found to vary linearly as a function of the logarithm of SO₂concentration in the range of 100 ppb–2 ppm at 600℃and the sensitivity (slop) was −23 mV/decade. In addition, the sensor coupled with ZnTiO₃-SE gave negligible re sponses to other interfering gases such as C₂H₂, CH₄, CO, NO₂, NO, NH₃. Furthermore, the present sensor possessed good repeatability, slightly affected by the change of oxygen concentration and relatively stability during 20 days of continuous high-temperature operation. Moreover, the polarization-curve measurements demonstrated that the good agreement between the observed sensitivity and the estimated value, confirming that the sensing mechanism was based on mixed-potential model.