Nanosized zinc oxide (ZnO) powders were prepared via DC thermal plasma process from microsized zinc powder while air was employed as a reaction gas. The ZnO nanopowders were characterized by X-ray diffraction, UV-Visible spectrometry, scanning electron microscope and energy dispersive X-ray analysis. The X-ray diffraction analysis of the sample showed the formation of nanopowder with wurtzite ZnO structure. The photocatalytic activities of ZnO powders were evaluated by measuring the degradation of Methylene Blue (MB) in water under the UV region. ZnO nanopowder resisted the growth of tested bacterias.