A simple surface modification technique was developed to functionalize polymeric and cellulosic materials with bactericidal polycationic groups. The poly(ethylene terephthalate) (PET) film was first graft copolymerized with 4-vinylpyridine (4VP) and subsequently derivatized with hexyl bromide via the quaternization of the grafted pyridine groups into pyridinium groups. The amount of pyridinium. groups on the film surface could be controlled by varying the 4VP monomer concentrations used for grafting. The pyridinium groups introduced on the surface of the substrate possess antibacterial properties, as shown by their effect on Escherichia coli (E. coli). The bacteria killing efficiency is very high when the concentration of pyridinium groups on surfaces is 15 nmol/cm(2) or higher. E. coli adhered on the functionalized surfaces are no longer viable when released into an aqueous culture medium. Filter paper, as a typical cellulosic material, was also functionalized in the same manner to introduce the pyridinium groups. The antibacterial activity was also similarly observed for this substrate. Thus, the present surface functionalization method has the advantage of being effective in conferring both polymeric and cellulosic materials with antibacterial properties.