The antibacterial and antibiofilm activities of cationic amphiphilic methacrylate polymers against cariogenic bacterium S. mutans were investigated. Cationic homopolymer PE and copolymer PE31 containing 31 mol % of ethyl methacrylate were synthesized by reversible addition-fragmentation chain transfer polymerization. These polymers displayed bactericidal activity toward S. mutans and prevented biofilm formation by killing the planktonic bacteria. At a concentration of 1000 mu g/mL when incubated for 2 h the polymers reduced >80% of biofilm biomass. When the polymer assay solution with the biofilm was vigorously mixed using a pipet for 30 s, >50% of biofilm mass was removed at polymer concentration of 250 mu g/mL. Chlorhexidine and a cationic surfactant failed to reduce the biofilm mass at the same concentration. PE0 was the most effective in removing biofilm and did not show any significant cytotoxicity to human gingival fibroblast and periodontal ligament stem cells when incubated for 10 min.