As an ethanol sensing material, the composites of In₂O₃-SnO₂were composed of In₂O₃microflowers and SnO₂nanoparticles. Both In₂O₃microflowers and SnO₂nanoparticles were synthesized by hydrothermal method and then mixed in an ultrasonic environment. The morphology and phase composition of the as-synthesized samples were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The results on gas sensing properties showed that when the mass ratio of In₂O3 and SnO₂was 2 : 1, the sensor based on the as-prepared In₂O₃-SnO₂composite exhibited high response and good selectivity to ethanol at 250℃. The response to 100 ppm ethanol gas was 53.2. UV illumination stabilized the responses of the sensors while the relative humidity increased. The gas sensing mechanism proposed was that the addition of SnO₂to In₂O₃enhanced the catalytic activity for the ethanol reaction, which changed the electrical resistance of the materials. Besides, the morphology was helpful to the gas reaction on the surface of the sensing materials.