An efficient procedure to prepare chitosan sorbate was established by using one two-step reaction.Firstly,sorbyl chloride was prepared by reflux of sorbic acid in thionyl chloride.Secondly,chitosan was selectively esterified with sorbyl chloride in MeSO3H.The chemical structure of the chitosan derivative was characterized by FT-IR and 1H-NMR analysis.The results showed sorbyl chloride mainly substituted with the hydroxyl group rather than amino group of chitsoan.The derivatives with DS of 0.44,1.21,1.93 were prepared with different molar ratio of chitosan and sorbyl chloride.The derivative(DS =1.21) manifested the strongest antimicrobial activity with the MIC of 0.125%,0.125% and 0.5(w/v) against Escherichia coli,Staphylococcus aureus and Aspergillus niger.