A viologen, N-hexyl-N'-(4-vinylbenzyl)-4,4'-bipyridinium dinitrate (HVVN), was synthesized and subsequently graft-copolymerized on poly(ethylene terephthalate) (PET) films. Silver nanoparticles can be deposited on the surface of the HVVN-PET film through photoinduced reduction of the silver ions in salt solution. The size and distribution of the silver nanoparticles can be varied by changing the reaction time. The pyridinium groups of the HVVN graft-copolymerized on the surface of the substrate possess bactericidal effects on Escherichia coli, and this antibacterial effect can be very significantly enhanced by the incorporation of silver nanoparticles on the HVVN-PET film. The dual fanctionalities of HVVN and silver remain stable after prolonged immersion in phosphate buffer solution and after aging in a weathering chamber.