Mixed potential NOx sensors for automotive exhaust were fabricated by using YSZ(yittria stabilized, zirconia) and oxide sensing materials. Through simultaneous response to NO2 and NO, sensing behavior of the sensors was studied at the temperature of 700 degrees C in 10% O-2 containing atmosphere. The EMF and I-V characteristics have been correlated with the NO/NO2 concentrations that are measured by gas analyzer in an effort to elucidate the sensing mechanism of oxide electrode.