Nano-sized zinc oxide particles were prepared from micro-sized zinc powder and oxygen as reacting gas by thermal plasma processing. As a process parameter the flow rate of the reacting gas was controlled and examined as photocatalysts for the UV-induced degradation of Methylene Blue in water solution. The research is focusign on the nano-sized ZnO to improve its photo-catalytic activity for removal of environmental pollutants. The characterization of the ZnO was analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and UV-vis spectrometer (UV-vis). The average particle sizes range from 30 to 100 nm.