The resistance of bacteria to antibiotics has caused serious threats to public health and it is urgent to develop novel antibacterial agents that do not induce drug resistance. Herein, a series of novel antibacterial copolymers, PCL16-b-Kn, mimicking the structure and action mechanism of natural antimicrobial peptides is reported. The diblock copolymers were synthesized via ring-opening polymerization and facile coupling reaction. The antibacterial results confirmed that the diblock copolymers possess superior antibacterial activities and exhibit rapid bactericidal action against both S. aureus and E. coli. A conclusion can be drawn that the antibacterial activity can be promoted by achieving a balance between the cationic and hydrophobic segments in the copolymers. Further hemolysis and cytotoxicity tests suggest the excellent biocompatibility of these diblock copolymers. Overall, our synthetic strategy demonstrates a new concept of designing novel biocompatible antibacterial copolymers and expands the categories of next-generation antibacterial agents without inducing drug resistance.