Abstract: Some properties of the dextran activated with bromine cyanide modified elastase were studied and compared, with those of natural elastase. Results showed that the enzymatic activity of elastase retained 94.6% of its original enzymatic activity after covalent modification with activated dextran. Modified elastase exhibited the same ability to resist hydrolysis by trypsin as the natural elastase. But its ability to resist hydrolysis by pepsin and denaturation by heat and acid was found to be higher than that of the natural elastase. These results suggest that the modified elastase may have greater merit in clinical applications than natural elastase.