Disclosed are a human serum albumin mutant that can be linked to a physiologically active protein to increase the stability of the protein in the blood, as well as a resulting protein produced by linking with the mutant. The protein produced by linking with the mutant consists of a human serum albumin mutant comprising the amino acid sequence set forth as SEQ ID NO:3 or an amino acid sequence that, in comparison with it, lacks not more than 10 amino acid residues and/or has not more than 10 amino acid residues replaced, with the proviso that the asparagine residue occurring at position 318 and the threonine at position 320 from the N-terminus of the amino acid sequence set forth as SEQ ID NO:3 are preserved and linked by peptide bonds via a single amino acid residue (X) except proline placed between those two amino acid residues, and a physiologically active protein linked to the mutant.