Antibacterial polymers of dimethylaminoethyl methacrylate benzyl ammonium chloride(DMAEMA-BC)with various molecular weights(MwS)were prepared under controlling radical polymerization conditions.The MwS of these polymers were determined by means of static multiangle laser light scattering and viscosity method.A Mark-Houwink equation was established to be[η]=0.154M0.764 for the Mw evaluation of poly(DMAEMA-BC)s.The effects of the Mws of these poly(DMAEMA-BC)s on their antibacterial activities against E.coli and S.aureus were investigated by various methods including viable cell counting,electrical conductivity titration,intracellular constituent leakage tests and electron microscopy.Our results indicate that the antibacterial efficiency of DMAEMA-BC was significantly enhanced after the monomers were polymerized into a polymer and increased obviously with the Mws,as a result of the increase of charge density.Further investigation of the molecular basis underlying the anti-bacterial role of these polymers revealed that poly(DMAEMA-BC)promoted the release of potassium ion from the membrane of bacterial cells and the release increased significantly with the Mws of the polymers used.