We report here a new-type zirconia-based sensor that can detect total NOx content at high temperatures such as 700 °C. A closed-one-end yttria-stabilized zirconia (YSZ) tube was used as a base sensor material. An oxide sensing electrode (SE) and a Pt counter electrode (CE) were formed on the outer and inner surfaces of the YSZ tube, respectively. The complex impedance of the device using a ZnCr2O4-sensing electrode was measured with an impedance analyzer in the frequency and the temperature ranges 0.1 Hz–100 kHz and 600–700 °C, respectively. A large semicircular arc was observed in complex impedance plots (Cole–Cole plots) in the lower frequency range examined and it seemed to correspond to the electrolyte/electrode interface. The impedance value at 1 Hz of the present device was found to vary almost linearly with the concentration of NO (or NO2) from 50 to 400 ppm in the sample gas at 600–700 °C. Furthermore, it is noted that the sensitivity of NO is almost equal to that of NO2. This means that the present device can detect the total NOx at higher temperatures. Keywords: NOx sensor, Complex impedance, Oxide electrode, Solid electrolyte, Stabilized zirconia, Car exhaust, ZnCr2O4