Mixed potential type solid-state electrochemical gas sensors using yttria-stabilized zirconia (YSZ) and columbite composite oxide sensing electrodes (SEs) prepared via a facile sol-gel method were developed for detection of sub-ppm acetone at 600℃. In the comparison of different devices, the sensor attached with CdNb2O6-SE displayed the highest response of 25 mV to 5 ppm acetone and even could achieve low detection limit of 200 ppb at 600 ℃. The fabricated sensor using CdNb2O6-SE exhibited rapid response and recovery times to 2 ppm acetone at 600 ℃, which are 9 and 21 s, respectively. Additionally, the present device also showed good repeatability, selectivity, wet-resistance and stability in 30 day measured periods at 600 ℃. Moreover, the sensing mechanism related to mixed potential was proposed and analyzed quantitatively and further demonstrated by polarization curve.