The sidewall modified single-walled carbon nanotubes (SWNTs) with amino-containing substituents were prepared using the radicals generated by the photolysis of acetonitrile. A subsequent treatment of modified SWNTs with the Ag colloid gave an attachment of Ag nanoparticles on the surface of SWNTs through the functionalized linkages. The Ag nanoparticle-modified SWNTs evaluated by antibacterial tests showed strong activities against Escherichia coli and Staphylococcus aureus. However, the use of Ag nanoparticle-modified SWNTs on simulated body fluid exhibited weaker antibacterial activity.