A solid-state amperometric NO sensor was investigated. High sensitivity was observed with the sensor consisting of La0.5Sr0.5MnO 3 and La0.4Sr0.6Mn0.8Ni 0.2O3 as inactive and active electrodes to NO oxidation, respectively, and La0.8Sr0.2Ga0.8Mg 0.1Ni0.1O3 as electrolyte. The sensor characteristics were studied in the temperature range 773-973 K and the highest sensitivity was found above 1800 μA/decade at 823 K. Because the current output of this sensor was little affected by coexisting gases, e.g., CO, H 2, C3H6, CO2, H2O, and NO2, it is expected that this sensor can detect NO in exhaust gas selectively. © 2005 The Electrochemical Society. All rights reserved.