NOx sensing properties of Ba2WO5 were investigated in an effort to explore for a new sensor material operative at high temperature. Ba2WO5 was prepared from BaO and WO3, and packed and sintered to fabricate disk-type sensor elements. It was found that the resistance of an element sintered at 800 degrees C decreased sharply upon exposure to NOx in air at 500 degrees C, exhibiting the sensitivity values (defined as the ratio of the resistance in air to that in the sample gas) as large as 47 and 29 to 200 ppm NO and 80 ppm NO2, respectively. The sensitivity was very dependent on the operating temperature, giving rise to a rather sharp maximum appearing at temperature around 500 degrees C. In addition, the elements sintered at the other temperatures (750, 850, or 900 degrees C) failed to exhibit significantly high sensitivity even at 500 degrees C. The NOx sensing mechanism of Ba2WO5 was briefly discussed. (C) 1999 Elsevier Science S.A. All rights reserved.