Quaternary ammonium compounds (QACs) have outstanding antimicrobial effect, but their immobilization onto cotton ber surfaces reminds a challenge. Herein, a QAC monomer, [2-(Methacryloyloxy) ethyl] trimethy lammonium chloride (DMC) was co-polymerized with methyl acrylate (MA) to prepare an antibacterial copolymer, poly(DMC-co-MA). To graft the copolymer with an improved grafting e ciency, cotton fabric was treated using carboxymethyl chitosan (CMC) to establish an aminofunctionalized ber surface rst. This treatment allows the amidation reactions between the amino groups and the pendant ester groups in the poly(DMC-co-MA) to take place, achieving a durable QAC coating onto the ber surfaces with remarkably antibacterial effect. Characterization results indicated that when DMC/MA monomer ratio was 100:1, the resulting copolymer endows the modi ed cotton fabric with antibacterial capability that inactivates all Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Even after 50 laundering cycles, more than 98.0% of the antibacterial rate could still be retained. Moreover, the wearing comfort properties such as softness, water absorption and air permeability of the nishing cotton fabrics have been insigni cantly changed by comparing to the untreated cotton fabric.