Excessive use of antibiotics accelerates the development and spread of drug-resistant strains, which is a huge challenge for the field of medical health worldwide. Quaternary ammonium salt polymers are considered to be membrane-active bactericidal groups with vast potential to control bacterial infections and inhibit drug resistance. Herein, we report on the creative synthesis and characterization of novel antimicrobial polymer nanocapsules based on pyridine quaternary ammonium salt. The antimicrobial polymer nanocapsules were formed by reaction of C3 symmetrical rigid monomer 2,4,6‑tris(4‑pyridyl)‑1,3,5‑triazine (TPT) and a flexible linker 1,2‑dibromoethane. The polymer nanocapsule was constructed as a cationic hollow sphere composed of a two-dimensional sheet whose main chain was formed by the pyridine quaternary ammonium salt, and a part of the bromide ion was adsorbed on the sphere. This hollow nanocapsule was characterized in detail by DLS, SEM, TEM, AFM, EDS and EA. When the cationic polymer nanocapsules are close to the Gram-negative Escherichia coli, the negatively charged phospholipid molecules in the bacterial membrane are attracted to the cationic surface and lead to rupture of cells. SEM confirmed the breakage of Escherichia coli membranes. The minimum inhibitory concentration was found to be 0.04 mg/mL, and the minimum bactericidal concentration was 0.1 mg/mL. Our experiments demonstrated that the adsorption of negatively charged phospholipid molecules on the surface of the pyridine quaternary ammonium salt polymer can kill Gram-negative bacteria without inserting quaternary ammonium salt hydrophobic groups into the cell membrane.