Tungsten oxide (WO3) nanocrystals with various nanomorphologies were synthesized by solvothermal method using tungsten hexachloride (WCl6) as a raw material and pure ethylene glycol (EG) or water-EG as reaction solvent, and the NO2-sensing properties of the WO3 nanocrystals were studied. The morphology and crystal structure were investigated by field emission scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The NO2 gas sensing properties of WO3 nanocrystals were investigated at different temperatures ranging from room temperature (25 degrees C) to 250 degrees C over NO2 concentration ranging from 0.1 to 3 ppm. The results indicate that the morphology and crystal phase of the WO3 nanocrystals depended on the water content in water-EG mixed solvent. With the increase of water content, the crystalline phase transformed from hexagonal to monoclinic. At the operating temperature below 55 degrees C, the sensor synthesized in EG solvent showed an abnormal p-type conductive behavior. It is found that all the sensors exhibit high sensor responses and rapid response characteristics to different concentrations of NO2, and their highest sensor responses are achieved at 100 or 50 degrees C. (C)( 2015 Elsevier B.V. All rights reserved.