The ZnO nanoparticles were synthesized by Nucleation-Crystallization Separation and co-precipitation. The structures and formed phase temperature of the samples were researched by X-ray diffraction (XRD) and DSC -TGA. Gas sensing properties of the samples were measured by a stationary state gas distribution method under static state. The results show that the ZnO prepared from Nucleation-Crystallization Separation has a higher response to 50 ppm ethanol and gasoline than ZnO prepared from co-precipitation. The sensitivity of ZnO prepared from Nucleation-Crystallization Separation to 50 ppm ethanol and gasoline are 34 and 68, which is better than the sensitivity of ZnO prepared from co-precipitation (17 and 28). The good sensing property may be due to the independence of nucleation and crystallization steps, which helps the more uniformity and thermal stability and the larger space utilization of ZnO particles.