THE PRESENT study was performed to investigate the …….antibacterial activities of silver nanoparticles (Ag-NPs) between gram negative Escherichia coli (E. coli) and gram positive Staphylococcus aureus (S. aureus) bacteria. The activity of Ag-NPs synthesized by physical method, this study was performed by observing the bacterial cells treated or not with Ag-NPs on bacterial conductivity, antibiotic susceptibility, molecular and morphological cellular structure by transmission TEM as results indicated that E.Coli and S. aureus treated with Ag-NPs can inhibit bacterial growth and significant increase in antibiotic susceptibility to protein, cell wall and DNA inhibitors. Results of dielectric relaxation and TEM indicated molecular and morphological changes. It will be concluded that Ag-NPs could be used as an excellent effective antimicrobial material on microorganisms.