NO x is one of dangerous air pollutants, and the demands for reliable sensors to detect NO x are extremely urgent recently. Conventional fluorite-phase YSZ used for NO x sensor requires higher operating temperature to obtain desirable oxygen ion conductivity. In this work, perovskite-phase Na 0.5Bi 0.5TiO 3 (NBT) oxygen conductor was chosen as the solid electrolyte to fabricate a novel highly sensitive NO 2 sensor with CuO as the sensing electrode and Pt as reference electrode. Na dopped Na 0.5Bi 0.5TiO 3 greatly improved the sensing performance of this sensor. The optimal sensor based on Na 0.51Bi 0.50TiO 3−δ exhibited good response-recovery characteristics to NO 2 and the response current values were almost linear to NO 2 concentrations in the range of 50–500 ppm at 400–600 °C. The response current value towards NO 2 reached maximum 11.23 μA at 575 °C and the value on NO 2 is much higher than other gases (CH 4, C 2H 4, C 3H 6, C 3H 8, CO), indicating good selectivity for detecting NO 2. The response signals of the sensor were slightly affected by coexistent O 2 varying from 2 to 21 vol% at 575 °C. The response current value decreased only 4.9% over 2 months, exhibiting the potential application in motor vehicles.