A new solid-state NO, sensor operative at high temperature was designed using stabilized zirconia and an oxide sensing electrode. Among the various oxides examined, CdMn2O4 was found to be the most excellent material for NOx sensing at 500 degrees C. The EMF values of the sensor were almost linear to the logarithm of NOx concentration with a positive slope for NO2 and a negative slope for NO. A, NOx sensing mechanism involving mixed potential was proposed based on the measurements of polarization curves.