PURPOSE: To obtain an org. product which contains amino acids in the form of oligopeptide refined by hydrolyzing whey protein, does not contain a protein of a specific mol.wt., ensures absorption and does not contain allergen. CONSTITUTION: Protein whey factions of soybean protein, etc., are prepd. as an aq. soln. and are subjected to prehydrolysis with pepsin preferably at pH2 to 3. These fractions are then subjected to enzymatically hydrolysis with tripsn- chymotrispsin and are ultrafiltered, concentrated and dried, by which the desired product contg. the amino acid as the ologipeptide form having 4 to 10 amino acids at a ratio of 40 to 60wt.% without contg. the protein of the mol.wt. of >=60000 is obtd.