The invention provides a method for measuring the protease activity of a transglutaminase-containing product comprising: mixing an aqueous solution (sample solution) of a transglutaminase-containing product and an aqueous solution of dimethylcasein in a prescribed ratio of transglutaminase activity to quantity of dimethylcasein, allowing the mixture to stand under prescribed conditions to cause a degradation reaction by protease to progress, adding an acid, filtering, and measuring the concentration of the protein in the filtrate. The invention is particularly useful for transglutaminase formulation for binding application and transglutaminase formulation for Surimi product.