Abstract: Aminated silver nanoparticles were prepared via surface-modification in situ, and the preparation conditions of nano silver were optimized. The nanoparticles were analyzed and characterized with UV-Vis spectroscopy, FT-IR spectrum, X-ray diffraction, Zeta potential and transmission electron microscopy. The antibacterial properties of nano silver were studied. It was found that the nanoparticles with positive charges could adsorb to negatively charged bacterial surface via electrostatic interaction and enhance bactericidal activity; aminated silver nanoparticles could efficiently inhibit the growth of Gram-positive and Gram-negative bacteria; and this kind of nanoparticles has a prospect of application in biomedical devices and antibacterial control systems.