To obtain a new physiologically active peptide having activities of acting on a human uterine muscle oxytocin receptor, etc.

This physiologically active peptide is a peptide containing a specific amino acid sequence, having specific physical and chemical properties and a physiological activity and is a substance acting on a human uterine muscle oxytocin receptor. The substance is useful for elucidating pathophysiology of maintenance of pregnancy, mechanism of delivery outbreak, miscarriage, etc., having a great number of unelucidated points. Since the peptide is a biological component, the peptide has a higher safety than that of a conventionally used medicine and a medicine provided with a diagnosing and treating effects having a specific action can be developed.