Potentiometric gas sensors using an anion-conducting polymer as an electrolyte and SnO2 loaded with or without 2.0 wt% Au as an electrode material were fabricated and the CO-sensing properties were investigated mainly in wet synthetic air (57% RH) at 30 degrees C. Loading of Au onto SnO2 powders by precipitation-deposition technique was quite effective in improving the sensing properties to CO and H-2, and the magnitude of CO response was larger than that of H-2 response. In addition, the CO response was largely dependent on concentration of O-2 in the gaseous atmosphere. These results indicate that electromotive force of the sensor is probably determined by mixed potential resulting from CO oxidation and O-2 reduction. Heat treatment of the Au-loaded SnO2 powder under reducing atmosphere decreased the H-2-sensing properties, and thus largely enhanced the CO selectivity against H-2. Especially, the sensor using Au-loaded SnO2 which was heat-treated in H-2 at 250 degrees C showed large CO response, the largest CO selectivity against H-2, and the fastest response and recovery speeds among all the sensors tested, while storage of the sensor under normal atmosphere weakened the effect of the heat-treatment in H-2 at 250 degrees C on the CO-sensing properties. (C) 2016 The Electrochemical Society. All rights reserved.