Abstract:Crayfish shells were utilized as the raw material for the extraction of chitin through sodium hydroxide/urea freeze-thawing combined with high-pressure steaming. The results showed that three cycles of freezethawing combined with high-pressure steaming（100 kPa，121 ℃，1 h）yielded chitin with the purity of 99.02%. The obtained chitin was used as the substrate for the preparation of chitosan via a reaction catalyzed by chitin deacetylase. After reaction with 1.0 U/mL chitin deacetylase and 1 mg/mL substrate for 12 h，the deacetylation degree of the obtained chitosan reached 92.62%. Furthermore，chitin and chitosan were characterized by scanning electron microscopy（SEM），Fourier transform-infrared spectroscopy（FTIR），and X-ray diffraction（XRD）.The results indicated that chitin had a loose structure，which facilitated the enzymatic reaction，and the preparation process affected the structure of chitosan. This approach avoided the use of large amounts of alkaline solution，had mild enzymatic reaction conditions，and produced chitosan with a high deacetylation degree.