Abstract: It is intended to provide a method for producing a denatured substance of lactalbumin, particularly the substance showing a cell death inducing activity against a tumor cell, simply at a low cost. The method for producing a denatured substance of lactalbumin includes heating a mixture of domestic animal milk and oleic acid. The method of the invention can produce a useful substance as a pharmaceutical which induces cell death of a tumor cell such as solid cancer or a leukemic lymphocyte from domestic animal milk which is an extremely inexpensive raw material and has advantages that the raw material can be obtained easily, supply of the raw material is stable, the raw material is inexpensive and the like. Further, the method is industrially advantageous because it has characteristics that a large amount of the tumor cell death inducing substance can be produced by a batch reaction, a column treatment is not required and the like.