Biodegradable poly(ester-phosphoester)s bearing multiple chloroethyl groups were synthesized facilely by the ring-opening copolymerization of 2-(2-chloroethoxy)-2-oxo-1,3,2-dioxaphospholane (CEP) and epsilon-caprolactone (CL) in the presence of lanthanum tris(2,6-di-tert-butyl-4-methylphenolate)s (La(DBMP)(3)) as single-component catalyst under mild conditions. Then the quaternization reaction was carried out between the halide copolymers and a series of N,N-dimethyl alkylamines to give poly(ester-phosphoester)s containing ammonium groups with various charge density and alkyl chain length. The antibacterial properties of these cationic poly(esterphosphoester)s were evaluated by OD600 and zone of inhibition methods against gram-negative (Escherichia coli) and gram-positive (Staphylococcus aureus) bacteria. Cationic poly(esterphosphoester)s with long alkyl chain on the ammonium groups show excellent antibacterial activity for both gram-negative and gram-positive bacteria even with low charge density. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3667-3673