With increasing troubles in bacterial contamination and antibiotic resistance, new materials possessing both biocompatibility and antimicrobial efficacy are supposed to be developed for future biomedical application. Herein, we demonstrated a chemo-enzymatic ring opening polymerization (ROP) approach for block copolyester, that is, poly(4-benzyl formate piperidine lactone-b-omega-pentadecalactone) (PNPIL-b-PPDL), in a one-pot two-step process. Afterward, cationic poly(4-piperidine lactone-b-omega-pentadecalactone) (PPIL-b-PPDL) with pendent secondary amino groups was obtained via acidic hydrolysis of PNPIL-b-PPDL. The resulting cationic block copolyester exhibited high antibacterial activity against Gram negative E. coli and Gram positive S. aureus, while showed low toxicity toward NIH-3T3 cells. Moreover, the antibacterial property, cytotoxicity and degradation behavior could be tuned simply by variation of PPIL content. Therefore, we anticipate that such cationic block copolymers could potentially be applied as biomaterials for medicine or implants.