The YSZ-based mixed-potential type gas sensor using CoTa2O6-SE was developed for NO2 detection at high temperature. The device utilizing CoTa2O6-SE sintered at 1000 °C gave the highest response of 93 mV to 100 ppm NO2 at 650 °C. The sensitivity of the fabricated sensor to NO2 in the concentration range of 5–500 ppm was 80 mV/decade. The fabricated sensor also exhibited good selectivity, stability and slight effect of oxygen and moisture at 650 °C.