Amphoteric terpolymers of acrylic acid (AA), acrylamide (AM), and N,N'-dimethyl-N-ethylmethacryloxylethylammoniumbromide (DMAEA-EB) with varied compositions P[AA-AM-(DMAEA-EB)] were synthesized by inverse Suspension polymerization. The components of P[AA-AM-(DMAEA-EB)] were verified by FTIR spectroscopy. The water absorption ability and antibacterial activity of the copolymer against Escherichia coli (E. coli) and Staphylococcus hyicus (S. hyicus) suspended in sterilized physiological saline were investigated. The introduction of -N+R4 may increase the water absorbency of P[AA-AM-(DMAEA-EB)] in some degree because of the excellent hydrophilicity of -N+R4. The AA-AM-(DMAEA-EB) hydrogels exhibited high antibacterial activity against bacteria tested. The process of adsorption between live bacteria cells and resins was at least partially reversible. A peak of antibacterial efficiency existed with increasing contact time. The resin killed 96.6%, E. coli organisms and 90.3% S. hyicus organisms, respectively, within 30 min of contact at dosage of 0.1g. The concentration of DMAEA-EB has a special effect on the antibacterial activity of the polyampholytic hydrogels, which is different from polycation. It was observed that the antibacterial activity of the resin with 2 mol%, of DMAEA-EB is superior to the copolymers tested with other compositions. (c) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 439-446, 2009