N-alkylated chitosan derivatives were synthesized in water containing acetic acid by the Michael addition reaction of chitosan with various acryl reagents. The chemical structures of the chitosan derivatives were characterized with Fourier transform infrared and H-1-NMR techniques. The H-1-NMR results indicated that the degree of substitution of the chitosan derivatives ranged from 0.13 to 0.39. The chitosan derivatives exhibited different solubilities in distilled water. X-ray diffraction analysis showed that the chitosan derivatives were amorphous. The chitosan derivatives still had antimicrobial ability. (c) 2008 Wiley Periodicals, Inc.