Abstract: Native trypsin and unfolded trypsin are modified by mono-6- deoxy-6- amino- β- cyclodextrin( CDAN) to improve their enzyme properties. The effect of CDAN modification on the relative activity,kinetic parameters,thermal stability,autolysis and stability in the urea of native trypsin and unfolded trypsin was studied. Results showed that there was an obvious decrease in the Kmvalue and increase in the catalytic efficiency( Kcat/ Km) of native trypsin and unfolded trypsin after modification.And the modified unfolded trypsin showed more obvious( p <0.05) change than modified native trypsin. The Kmvalue of unfolded trypsin was 0.35 × 10- 3mol / L and 0.11 × 10- 3mol / L before and after modification,respectively. After modification the relative activity of native trypsin increased from 2.1% to 58.3% at incubation 10 min at 60 ℃,while that of unfolded trypsin increased from 19.5% to 70.5%.Moreover,before and after modification,the relative activity of native trypsin was 11.3% and 78.8% at incubation 60 min in urea solution,respectively,while that of unfolded trypsin was 21.3% and 84.9%,respectively. The results showed that unfolded trypsin showed more obvious improvement in the thermal stability,autolysis and stability in the urea after modification in comparison to native trypsin.