In this paper, g-C 3 N 4 -WO 3 composite materials were prepared by hydrothermal processing. The composites were characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and N 2 adsorption-desorption, respectively. The gas sensing properties of the composites were investigated. The results indicated that the addition of appropriate amount of g-C 3 N 4 to WO 3 could improve the response and selectivity to acetone. The sensor based on 2 wt% g-C 3 N 4 -WO 3 composite showed the best gas sensing performances. When operating at optimum temperature of 310°C, the responses to 1000 ppm and 0.5 ppm acetone were 58.2 and 1.6, respectively, and the ratio of the S 1000 ppm acetone to S 1000 ppm ethanol reached 3.7.