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Zinc oxide nanoparticles (ZnO-NPs) are versatile inorganic metal oxide nanoparticles known widely, which use in a broad spectrum of the applications. In this study, chemical method was used to prepare ZnO-NPs.The shape and size of the prepared nanomaterial were visualizedbya transmission electron microscope (TEM). The average length and diameter of the prepared ZnO-NPs were approximately100-200 nm and 25-50 nm, respectively. In vitro, the prepared ZnO-NPs were used as an anticancer agent toward breast cancer cell lines (MCF-7). However, the results of MTT assay showedthat ZnO-NPs is a promising drug against MCF-7. The prepared ZnO-NPs was also tested as an antimicrobial agent against (gramnegative and gram positive) bacteria. Escherichia coli (E. coli) and Staphylococcus aureus (S.aureus) were selected as a test ofbacteria. The antibacterial profile of the prepared ZnO-NPs was also studied with different concentration of ZnO-NPs with different methods such as a disc method, well diffusion agar method, minimum bactericidal concentration (MBC) and minimum inhibitory concentration (MIC).Moreover, an effect of time with different concentrations of Zn-ONPs at the growth of S. aureusand E. coliwas studied. Five different concentrations of ZnO-NPs were tested to determine the MICthatincludes 15, 10, 5, 2.5, 1, and 0.5mg/ml. The MIC valueswere found to be 1 and 0.5 g/m for E. coli and S. aureus, respectively. The resistivity against gram-positive bacteria wasless as compared with gram negative bacteria. IncreasingZnO-NPs concentration was relatedwithhigh antibacterial activity of ZnO-NPs. The antibacterial effect of ZnONPs was depending on a time and the effect was gradually.