The present invention provides stable metastin derivatives having excellent biological activities (a cancer metastasis suppressing activity, a cancer growth suppressing activity, a gonadotropic hormone secretion stimulating activity, sex hormone secretion stimulating activity, etc.). By substituting the constituent amino acids of metastin with specific amino acids, the metastin derivatives of the present invention achieve more improved blood stability, solubility, etc., reduced gelation tendency, improved pharmacokinetics, as well as exhibit an excellent cancer metastasis suppressing activity or a cancer growth suppressing activity. The metastin derivatives of the present invention also have a gonadotropic hormone secretion suppressing activity, sex hormone secretion suppressing activity, etc.