The synthesis and antibacterial properties of N-halamine copolymers are reported in this paper. 3-(4'-vinylbenzyl)-5,5-dimethylhydaiitoin (VBDMH) monomer and its copolymers with n-butyl methacrylate (BMA) were prepared under mild conditions. The effects of monomer feeds on the composition of the final copolymers and reaction conversion were investigated. It was found that VBDMH had higher reactivities than BMA in the copolymerization reactions and the reactivity ratios of VBDMH and BMA were calculated to be 8.91 and 0.42, respectively, according to the Fineman-Ross equation in the preparation of PBMA-co-VBDMH. Two chlorination methods were applied and compared in the process of polymers chlorination. After chlorination by tert-butyl hypochlorite, the polymers provided powerful antibacterial activities against Escherichia coli (E. coli). The surface morphologies of the chlorinated polymer films used in antibacterial assessment were observed by scanning electron microscope. The copolymers before and after chlorination were characterized with fourier transform infrared (FTIR) and H-1-nuclear magnetic resonance (H-1-NMR). Their thermal properties were analyzed with thermogravimetric analysis (TGA) studies.