Disclosed are a human serum albumin mutant that links with a bioactive protein and can increase the stability of the protein in the blood, and a protein linked thereto. A human serum albumin mutant including a linked protein that is an amino acid sequence shown by SEQ ID NO: 3 or an amino acid sequence in which 10 or fewer amino acid residues have been deleted and/or 10 or fewer amino acid residues have been substituted in SEQ ID NO: 3, wherein the amino acid sequence is conserved in a state in which the asparagine residue 318 and the threonine residue 320 from the N terminus of the amino acid sequence shown by SEQ ID NO: 3 are linked by a peptide bond via a single amino acid residue (X) other than proline between these two residues； and a bioactive protein linked thereto.
