Antibacterial activity of chitosan, and a graft copolymer based on chitosan namely chitosan-graft-poly(N-vinyl imidazole), (Chi-graft-PNVI), was studied against Staphylococcus epidermidis (S. epidermidis) and Escherichia coli (E. coli). The graft copolymer was prepared by two different methods; via an N-protection route and without N-protection to observe the effect of free amine groups on the antibacterial activity. It was further investigated whether a combination of each of these products would produce a synergetic effect with the antibiotic gentamicin against S. epidermidis and E. coli compared to gentamicin alone. Antibacterial activity was determined by the inhibition zone measurement method. Results reveal an improvement in the antibacterial activity of gentamicin, when combined with chitosan or chitosan-based biomaterials against S. epidermidis and E. coli compared to that of gentamicin itself. When gentamicin is used in combination with Chi-graft-PNVI prepared via N-protection, antibacterial activity against S. epidermidis is three times higher in comparison with the activity of gentamicin alone according to the inhibition zone measurements. Gentamicin produces an inhibition zone of 8.2 +/- A 0.2 mm against S. epidermidis when undiluted, while the inhibition zone increases to 25.8 +/- A 0.7 mm in combination with Chi-graft-PNVI prepared via N-protection. These combinations have a potential to form a basis for new formulations of gentamicin with improved antibacterial activity and might allow usage of decreased doses of the antibiotic.