PROBLEM TO BE SOLVED: To provide an IL(interleukin)-11 functionally modified by: clarifying the relationship between biological activity of the IL-11 and structure thereof and modifying a moiety involved in the biological activity.SOLUTION: This invention relates to the IL-11 modified by adding an amino acid or a peptide, wherein the IL-11 thus modified may be the one to which one amino acid is added to an IL-11 to be modified, or may be the one to which a peptide consisting of a plurality of amino acids, such as 3 to 8 amino acid residues, is added to the IL-11 to be modified.
