In this study, we used different molecular weights chitosan, to graft chitosan onto cotton fabrics with citric acid. We researched the impact of cotton fabric surface by the graft ratio, the physical properties, and the antibacterial activity by processing graft reaction with the different concentrations of critic acid. The results showed us the stiffness of cotton fabrics was improved by increasing concentration of citric acid, but the tensile strength of cotton fabrics was decreased. Besides, by grafting chitosan onto cotton fabrics, the grafted cotton fabrics would be with antibacterial activity against Staphylococcus aureus.