N,N-dimethyl-O-quaternary ammonium chitosan(NNQAC) was synthesized from chitosan by N-dimethylation then quaternized by 2,3-epoxy propyl trimethyl ammonium chloride. The structure of NNQAC was characterized by FTIR. Properties of quaternary ammonium chitosans, including solubility, antimicrobial activity, water-absorption and water-retention ability, were investigated. The results showed that NNQAC was water–soluble in neutral and basic environments. The moisture-absorption and retention abilities of NNQAC were higher than that of chitosan and equivalent to hyaluronic acid. The antibacterial activities of NNQAC were tested against Bacillus subtilis, Escherichia coli and Staphylococcus aureus. In water medium, NNQAC exhibited MIC values in the range of 10 to 2.5 μg/mL.