A rapid assay method of collagenase activity has been developed using (14)C-labeled soluble collagen as substrate. This method is based on following three parts; first, carrying out the enzyme reaction with (14)C-labeled collagen in solution containing 0.25M glucose to prevent collagen fiblil formation at 35℃ under neutral condition, second, denaturation of the enzyme digestion products at 35℃ for 1hr after stopping the reaction by adding o-phenanthroline and third, selective extraction of the denatured (14)C-products into dioxane at a final concentration of 50 % and counting (14)C-activity in the surpernatant. The rate of the reaction was about 10 times higher than that obtained by the conventional method using reconstituted collagen fiblils as substrate and relationship between enzyme activity and enzyme concentration was linear over a wider range regardless of the purity of collagenase.