Inspired by mussel-adhesion phenomena in nature, we present a simple, mild and green method to prepare polystyrene/Ag (PS/Ag) nanocomposite particles with enhanced antibacterial activities. In this approach, monodisperse polystyrene particles are used as template spheres, which are then coated with polydopamine (PDA) through the self-polymerization of dopamine in a weakly alkaline aqueous environment (pH = 8.5). Silver precursor-[Ag(NH₃)₂]⁺ ions are added and absorbed onto the surfaces of the PS/PDA composite spheres by the active catechol and amine groups of the polydopamine coating. Meanwhile, these adsorbed [Ag(NH₃)₂]⁺ ions are in situ reduced into metallic silver nanoparticles by the “bridge” of the polydopamine coating, and the formed Ag nanoparticles are home positioned. As polydopamine is an environmentally friendly reagent with abilities as a universal adhesive to any surface and as a mild reductant for noble metal salts, because of its abundant active catechol and amine groups, neither additional reducing and toxic reagents nor special surface modifications of the template are needed in this procedure. Moreover, preliminary antibacterial assays indicate that these PS/Ag nanocomposite particles show enhanced antibacterial activities against Escherichia coli (Gram-negative bacteria) and Staphylococcus aureus (Gram-positive bacteria), while they do not show significant in vitro cytotoxicity against HEK293T human embryonic kidney cells. These results suggest that these PS/Ag nanocomposite particles could be promising antibacterial materials for future biomedical applications.