This investigation was done to evaluate the bactericidal efficiency of silver nanoparticles (Ag-NPs) against methicillin-resistance Staphylococcus aureus (MRSA) and methicillin-susceptible Staphylococcus aureus (MSSA) strains. The strains were previously isolated and obtained from milk and its surrounding animal milking environment from 60 dairy cattle houses including 30 houses for cows and 30 houses for buffalos. Ag-NPs solution was prepared and MIC (minimal inhibitory concentrations) and MBC (minimal bactericidal concentration) were determined. The obtained results showed that the mean values of MIC and MBC of Ag-NPs against MRSA were 23.44±0.21 and 31.25±0.26 µg / ml, respectively; while the mean values of MIC and MBC of Ag-NPs against MSSA were 11.33±0.14 and 13.28±0.17 µg / ml, respectively. The statistical analysis showed that no significant difference between the effect of Ag-NPs on MRSA and MSSA (p < /em>> 0.05), as the bactericidal activity of Ag-NPs was not affected by the resistant mechanisms to methicillin. It can be concluded that Ag-NPs have potent bactericidal activity against MRSA as well as MSSA strains.