Uniform and monodisperse ZnSn(OH)6 perfect octahedrons have been synthesized by a facile coprecipitation reaction process. The particle size of the as-prepared ZnSn(OH)6 octahedral structure can be readily controlled by adjusting the reaction temperature (T), and the side length of ZnSn(OH)6 octahedrons was tailored from 3 μm (40°C) to 4 μm (60°C) and 5 μm (80°C). The ethanol sensing properties of ZnSn(OH)6 octahedrons were carefully investigated. The gas sensing experimental data show that the sensor based on ZnSn(OH)6 (40°C) has good selectivity, fast response/recovery time and the highest response (Ra/Rg = 23.8) to 200 ppm ethanol at relatively low optimum operating temperature (200°C) compared to sensors based on ZnSn(OH)6 (60°C) and ZnSn(OH)6 (80°C), which might result from different specific surface areas. The study demonstrated that perfect octahedral ZnSn(OH)6 with controlled crystalline size and desirable sensing performance can be synthesized by a simple fabrication procedure, and the octahedral ZnSn(OH)6 could be a highly promising material for high-performance sensors.