Abstract: Providing is a new enzyme assay method for enzymes having a water-insoluble or substantially water-insoluble substrate. In the method for measuring enzymatic activity, a prescribed amount of an enzyme is disposed on a part of the surface of a gel comprising dispersoids, at least some of which are the substrate of the enzyme. Recesses formed in the surface of the gel by the action of the enzyme are measured, and the enzyme activity is calculated on the basis of the measurement results and the amount of the enzyme. The measurement of the recesses formed in the surface of the gel is performed using a method for measuring the shape and the volume of the recesses, a method for measuring changes in the optical transmittance of the gel due to the formation of the recesses, or a method for measuring changes in the optical reflectance of the gel surface due to the formation of the recesses.