The diversity of structure and physiological activity of non-protein amino acids is briefly described. Some peptides containing non- protein amino acid residues are introduced and the essential roles of these residues are discussed. Recent progress in modifying the bioactive peptides with non-protein amino acids and their preferences are generally reviewed.

Key words: NON-PROTEIN AMINO ACID, POLYPEPTIDE, BIOACTIVE SUBSTANCE, STRUCTURE ACTIVITY RELATIONSHIP, MODIFICATION, ANTAGONIST, KINETIN