The present invention relates to a fusion protein or peptide the in vivo half-life of which is increased by maintaining in vivo sustained release and to a method for increasing in vivo half-life using same. A fusion protein or peptide according to the present invention has excellent in vivo stability by binding a physiologically active protein or physiologically active peptide to an alpha-1 antitrypsin mutant or alpha-1 antitrypsin mutant with one or more amino acids mutated to maintain the in vivo sustained release and to significantly increase the half-life thereof in blood (T1/2) compared to an inherent physiologically active protein or physiologically active peptide. Thus a fusion protein or peptide according to the present invention can be useful in developing a sustained-release preparation of a protein or peptide drug.
