Provided is a method for producing an economical bovine serum composition containing many factors useful for cell proliferation. The method includes a step of performing an anticoagulation treatment of bovine whole blood with an anticoagulant, a step of obtaining a buffy coat and a fraction with a heavier specific gravity than that of the buffy coat from the anticoagulated whole blood, and a step of promoting and activating an interaction between the obtained leukocytes and platelets at a given temperature for not less than a given time to cause secretion or release of a humoral factor from the leukocytes and/or platelets and performing a recoagulation treatment of blood components including the humoral factor with a re-coagulating agent.
