Monodispersed ZnSnO3 microspheres are successfully prepared via a facile microwave-assisted method together with subsequently calcination treatment. Powder X-ray diffraction (PXRD) results indicate that the structure of the products shifted from crystalline to amorphous under high-temperature treatments. Field emission scanning electron microscope (FESEM) and the transmission electron microscope (TEM) observations demonstrate that the as-obtained products are composed of uniform microspheres with rough surfaces and the mean diameter is measured as～700 nm. Moreover, the morphology of ZnSnO3 microspheres can be well controlled by adjusting the ratio of Zn2+and Sn4+. The gas sensing properties of ZnSnO3 microspheres with different ratios of Zn2+/Sn4+ are investigated. Our results indicate that the ZnSnO3 microspheres exhibit good selectivity and high sensitivity towards ethanol at the optimum working temperature of 230 ℃. When the sensor is exposed 50 ppm ethanol, the value of response is 47 and the response/recovery times are 11 s and 12 s, respectively.