A solid-state amperometric NO sensor was investigated. High sensitivity was observed with the sensor consisting of La0.5Sr0.5MnO3 and La0.4Sr0.6Mn0.8Ni0.2O3 as inactive and active electrodes to NO oxidation, respectively, and La0.8Sr0.2Ga0.8Mg0.1Ni0.1O3 as electrolyte. The sensor characteristics were studied in the temperature range 773-973 K and the highest sensitivity was found above 1800 mu A/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. (C) 2005 The Electrochemical Society.