Abstract: By determining viscosity average molecular weights of degradation products of chitosan by α-amylase,cellulose and lipase,the degradation conditions of the three enzymes were optimized respectively. The results showed that the optimal conditions of α-amylase degradation are 120 min,temperature 45 ℃ and enzyme amount 1400 U/g,the optimal conditions of cellulose degradation are time 75 min,temperature 45 ℃ and enzyme amount 400 U/g,and the optimal conditions of lipase degradation are time 90 min,temperature 45 ℃ and enzyme amount 800 U/g. The molecular weight below 2000 chitosan is obtained,which can be used for the further study on complex between chitosan oligosaccharide and metal ion.

Key words: chitosan； degradation； &alpha, -amylase； cellulose； lipase