ZnO nanoparticles with an average size of about 20-40nm has been synthesized by thermal treatment of ZnS nanoparticles in an air atmosphere. The ZnS nanoparticles has been synthesized at a low temperature of 60℃ by using zinc acetate as a zinc source and TAA as a sulfur source with the aid of ultrasonic. The as-prepared products were characterized by Fourier transformed infrared spectra（FT-IR）, Thermal gravimetric analysis and differential thermal analysis（TGA-DTA）, X-ray diffraction study（XRD）, Field-emission scanning electron microscopy（FE-SEM）, Transmission electron microscopy(TEM), EDS and Photoluminescence (PL) spectra , respectively. The results have revealed that the ZnO nanoparticles are of hexagonal wurtzite structure, of high crystallinity and the size of the ZnO nanoparticles had an decreasing trend with the increment of the ultrasonic time. The room temperature PL spectra showed three strong emissions with peaks located in the range of 400～550nm.