<p>Recently, bio-safe germicidal ZnO has been attracting much attention because of the interaction with various biomolecules chemically as well as physically. As its antibacterial activity is related to reactive oxygen species (ROS), the ROS have been investigated in terms of luminol chemiluminescence (CL) emitted from the ZnO surface. In this study, the relationship between the disinfect activity of four kinds of ZnO powders and their physico-chemical properties has been studied using XRD (X-Ray Diffraction), SEM (Scanning Electron Microscope), BET (Brunauer–Emmett–Teller), CL, ESR (Electron Spin Resonance), and XPS (X-ray Photoelectron Spectroscopy) and bio-test using E. coli. Four ZnO powders tested were as following; No. 1 is newly developed ZnO, prepared via hydrothermal treatment in aqueous Zn(NO₃)₂ solution and then re-oxidized, which reveal a strong antimicrobial activity under dark conditions; No. 2 starting material for No. 1, derived from zinc acetate; No. 3 fine ZnO prepared at low-temperature heating of basic zinc carbonate; No. 4 conventional fine ZnO synthesized from vaporized metal Zn in air. All powders revealed antimicrobial activity in the dark; different amounts and kinds of ROS have been emitted from each ZnO powder, however, it has been cleared that its sustainability depends significantly on the contents of interstitial Zn contained in ZnO particles.</p>