Problem to be solved. To provide a method for efficiently producing a casein enzyme treated product containing high levels of a tripeptide consisting of Met-Lys-Pro and having emulsifying properties. Solution. The method for producing a casein enzyme treated product containing a tripeptide consisting of Met-Lys-Pro is characterized by using a proline-specific endoprotease concentration of 0.1 to 3 U/g to casein as a raw material. The content of the tripeptide consisting of Met-Lys-Pro (mg/1 g of casein enzyme treated product) is 0.9 to 1.3 mg/g in the casein treated product. From the casein enzyme treated product, a fraction is obtained having a molecular weight of 1,000 Da or less containing the tripeptide consisting of Met-Lys-Pro.