The core-shell structure SiO2@Ag nanoparticles were synthesized by a facile chemical reduction method. Firstly, the mercapto- silica spheres had been prepared by the stober method, in which 3-mercaptopropyltrimethoxysilane (MPS) was used as a sole silica source. The reaction involves mixing the MPS precursor, ammonia in aqueous solvent at room temperature. Secondly, the core-shell structure SiO2@Ag nanoparticles were synthesized by reducing AgNO3 on the surface of mercapto-silica spheres in the presence of the reducing agent. The core-shell structure SiO2@Ag nanoparticles were investigated by means of ultraviolet–visible absorption spectroscopy (UV-vis), high resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Antibacterial properties of the as-synthesized SiO2@Ag nanoparticles were investigated using both Gram negative of Escherichia coli (E. coli) and Gram positive of Staphylococcus aureus (S. aureus) as bacterial strains. The results show that the coreshell structure SiO2@Ag nanoparticles exhibit excellent antibacterial properties against E. coli and S. aureus bacteria.