The water soluble and reactive O-methyl acrylamide quaternary ammonium salt of chitosan (NMA-HTCC) was prepared with a view to develop an antibacterial finishing on cotton fabric. 2-hydroxypropyltrimethyl ammonium chloride chitosan (HTCC) was synthesized by the chemical reaction of chitosan and 2,3-epoxypropyltrimethyl ammonium chloride. Then, NMA-HTCC with reactive groups was synthesized by the chemical reaction of HTCC and N-(hydroxymethyl) -acrylamide, and its chemical structure was characterized by the Fourier transform infrared spectroscopy and nuclear magnetic resonance (NMR). The antibacterial activities of chitosan and NMA-HTCC were tested and compared by the minimal inhibitory method. Cotton fabrics were finished by NMA-HTCC under the alkalinity condition using sodium bicarbonate as the catalyst. The antibacterial activity of cotton fabric before and after finishing was measured by the oscillation flask method. The results showed that both chitosan and NMA-HTCC had a significant antibacterial effect on staphylococcus and coli, and the antibacterial activity of NMA-HTCC was better than that of chitosan. The antibacterial activity of cotton fabric to staphylococcus and coli were significantly improved after finishing by chitosan and NMA-HTCC, and the antibacterial activity of the cotton fabric finished by NMA-HTCC was better than that finished by chitosan.Keywords reactive quaternary ammonium salt of chitosan, O-methyl acrylamide quaternary ammonium salt of chitosan, cotton fabric, antibacterial activity Chitosan has been widely used in many fields, such as the textile industry, daily environmental protection, biological medicine and so on due, to its biocompatibility, degradability, lack of antigenicity, adsorption and so on. 1-3 However, chitosan cannot be dissolved in water and organic solvent, and can only be dissolved in acid solution, which greatly limits its application. Therefore, where solubility in water at neutral or high pH is required, it is necessary to improve chitosan solubility by chemical modification. As one of the important modification methods of chitosan, alkylation modification has been widely researched and applied. 4-7 Chitosan quaternary ammonium salt, with strong antibacterial ability and good moisturizing property, can be dissolved in acid, neutral and alkaline conditions. It has been widely applied in medicine and health, wastewater treatment and so on, 8,9 but so far there has been little study on the application of the chitosan quaternary ammonium salt for textile finishing. Based on the good water-solubility and biocidal properties of quaternary ammonium salt of chitosan, 2-hydroxypropyltrimethyl ammonium chloride chitosan (HTCC) was synthesized using chitosan and 2,3-epoxypropyltrimethyl ammonium chloride, and then HTCC reacted with N-