ZnO nanoparticles were synthesized in the method of precipitation, and they were characterized by the means of the transmission electron microscopy (TEM), the X-ray powder diffraction (XRD), the thermogravimetric analysis and differential thermal analysis (TG-DTA), and the Fourier transform infrared spectroscopy (FT-IR). Also their photocatalytic and degradation performance for the methyl orange aqueous solution were studied. The research results showed as-prepared ZnO nanoparticles were spherical crystals in hexagonal crystal system, and their size distribution was mainly in the range of 20-30 nm. The annealing temperature was about 390 °C, and a few organics remained, which may be helpful for the formation of ZnO particles. They had integrated crystal form, high crystallinity and thermal stability. Moreover, the obtained ZnO nanoparticles had excellent photocatalytic and degradation performance for the methyl orange aqueous solution. When reacted for 3.5 h, the degradation rate of the methyl orange aqueous solution was up to about 97%.