The current spreading of nanomaterial applications supports the search for further possible functions of theses diminutive particles. The antibacterial potentiality of zinc oxide (ZnO) nanoparticles (NPs) againstS. aureus causing mastitis was evaluated using qualitative and quantitative assays. These tests were performed in nutrient broth and nutrient agar following standard methods. In addition, the effect of different concentrations of ZnO nanoparticles on the growth of S. aureus was measured.MIC was determined using six different  concentrations of ZnO nanoparticles including  16,  8,  4,  2,  1  and  0.5 mg/ml.  The  MIC  value S. aureus  was  0.5  mg/ml.  The  results  showed that ZnO  nanoparticles have  antibacterial  inhibition  zone  of 29 mm at  the  concentration  of 10 mg/ml against S. aureus., and the antibacterial  activity of ZnO nanoparticles  increased  with  increasing  powder  concentration in vitro.