New type NOx sensors were newly designed by using stabilized zirconia and an oxide sensing electrode. Among the various oxides examined for the sensing electrode, CdMn2O4 was found to be the most excellent material. Both planar and tubular devices attached with a sputtered CdMn2O4 layer could respond well to NO2 as well as NO in air at higher temperature, such as 500 degrees C. The EMF values of the devices 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.