In　this　work,　single　electron　transfer　living　radical　polymerization　(SET-LRP)　was　used　to　functionalize　chitosan　in　a　well-controlled　manner.　The　chitosan-based　macroinitiator　was　first　synthesized　and　then　initiated　the　SET-LRP　of　methacryloyloxyethyl　trimethylammonium　chloride　(DMC)　in　ionic　liquid　system,　using　Cu-0/N,N,N,N,N-pentamethyldiethylenetriamine　as　a　catalyst.　The　grafting　of　PDMC　brushes　on　chitosan　was　confirmed　and　analyzed　by　Fourier　transform　infrared　spectroscopy　and　H-1　nuclear　magnetic　resonance.　Transmission　electron　microscopy　reveals　that　the　chitosan　copolymer　showed　self-assembled　behavior　in　acetone.　Surface　properties　of　the　copolymer　have　been　investigated　by　environment　scanning　electron　microscopy　analysis.　The　linear　relationship　between　the　ln([M](0)/[M](t))　and　time,　the　linear　increase　of　number-average　molecular　mass　with　conversion　as　well　as　the　low　polydispersity　index　of　the　polymer　confirmed　the　living/controlled　features　of　the　polymerization　of　DMC　through　SET-LRP.　Finally,　the　chitosan　copolymer　demonstrates　its　potential　antibacterial　application,　showing　excellent　inhibitive　capability　against　Escherichia　coli.　(c)　2015　Wiley　Periodicals,　Inc.　J.　Appl.　Polym.　Sci.　2015,　132,　42754.