Synthetic amphiphilic poly(vinyl ester) copolymers of vinyl N,N-dimethylethylglycinate with vinyl alkanoate esters can show very high antibacterial activities. The copolymers contain a positive charge one carbon away from the ester group and alkane side chains in the size range from methyl to hexyl groups. A copolymer (degree of polymerization as 9) with 37 mole% of hexyl side chains showed high antibacterial activities in terms of minimum inhibitory concentrations (31 μg mL⁻¹ against Escherichia coli and 16 μg mL⁻¹ against Staphylococcus aureus) and an unusually high hemolytic activity. Compared with its isomeric polymethacrylates, this extremely high hemolytic power of poly(vinyl ester) can be attributed to its more accessible CO dipole orientation for hydrogen bond formation and dipole–dipole interaction with the cell surface.