Disclosed is a method for producing a fraction containing a branched amino acid at a high content from a proteolytic product in a simple manner and in large quantity. A polar organic solvent is added to an aqueous solution of a proteolytic product containing a branched amino acid at a final concentration of 70 v/v% or more to collect a supernatant containing the branched amino acid at a high concentration. It is preferred that the pH value at the fractionation is 4 to 10, the decomposition ratio of the proteolytic product used is 90% or more, and the content of a free amino acid is 50% or less.
