© 2015 Elsevier B.V. In the present work, gas-sensing properties of flame-spray-made Co-doped SnO2 nanoparticles are systematically studied for detection of nitric oxide (NO), acetone (C3H6O) and ethanol (C2H5OH) gases occurred in human breathe. Structural characterizations by electron microscopy and X-ray analysis confirmed the formation of loosely agglomerated SnO2 nanoparticles (5-20 nm) with highly crystalline tetragonal-cassiterite SnO2 structure and Co substitutional doping with Co2+ and Co3+ oxidation states. The gas-sensing properties of unload SnO2 and Co-doped SnO2 sensors were systematically tested towards NO, acetone and ethanol. Tested results indicated that small Co-doping levels in the range of 0.2-0.5 wt% led to enhanced sensing properties toward NO, acetone and ethanol compared with undoped one. In particular, 0.2 wt% Co-doped SnO2 sensor showed very high response of ∼1637-1000 ppm NO at 350 °C while 0.5 wt% Co-doped SnO2 one exhibited high responses of ∼660-2000 ppm acetone and ∼806-1000 ppm ethanol. Thus, Co-doped SnO2 sensors are potential for responsive detections of NO, acetone and ethanol at ppm-level but with limited selectivity and may be useful for general environmental, industrial and biomedical applications.