Amphoteric polymer hydrogels were prepared by the copolymerization of three kinds of N,N'-dimethyll-N-alkylmethacryloxylethyl ammoniumbromide (DMAEA) with different lengths of alkyl chains (DMAEA-RB) (R-ehtyl/hexyl/dodecyl), acrylic acid (AA), and acrylamide (AM). The water content of the AA-AM-(DMAEA-RB) terpolymers decreased with the increasing length of alkyl chains in quaternary ammonium group in the terpolymers and increased with the increasing molar ratio of DMAEA-RB to 2 mol % and then decreased. Their antibacterial activities against Escherichia coli and Staphylococcus hyicus were investigated by a colony count method. It was found that the copoly-mer exhibited higher antibacterial activity with increasing chain length of alkyl groups in ammonium groups. For P[AA-AM-(DMAEA-DB)], the DMAEA-DB content is higher and contact time is longer, its antibacterial activity is better. However, when the contact time and quaternary ammonium content were above 30 min and 2%, respectively, the amount of live cells N(t) in a cell suspension increased in the presence of P[AA-AM-(DMAEA-EB)] or P[AA-AM-(DMAEA-HB)]. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 1767-1773, 2011