A peptide of the following (I) or (II). (I) a peptide represented by the formula B, A-B, B-C or A-B-C in which A, B and C each is represented by the following (1), (2) and (3) and, when it is bonded to other object peptide, it is able to extent the half-life in plasma as compared with the object peptide where the physiological activity of the object peptide is still retained. (II) a peptide comprising a reversed sequence of the peptide of (I)； a sequence which is represented by A-B in (I) and A or B is reversed； a sequence which is represented by B-C in (I) and B or C is reversed； or a sequence which is represented by A-B-C in (I) and A, B, C, A and B, B and C or A and C is reserved. (1) A is a peptide comprising 1 to 14 of any amino acid(s) (2) B is a peptide represented by the formula 1: (Wk-X1-Y-Zm-Wn)-(Wo-Xp-Y-Zq-Wr)s (In the formula 1, W is a basic amino acid； X and Z are any amino acids； Y is an acidic amino acid； k is 1 or 2； 1 is an integer of 4 ‰¥ 1 ‰¥ 0； m is an integer of 2 ‰¥ m‰¥ 0； 4 ‰¥ 1 + m ‰¥ 0； n is 1 or 2 ； O is 1 or 2； p is an integer of 4 ‰¥ p ‰¥ 0； q is an integer of 2 ‰¥ q ‰¥ 0； 4 ‰¥ p + q ‰¥ 0； r is 1 or 2； and s is 0 or 1.) (3) C is a peptide comprising 2 to 14 of any amino acids.
