The present invention provides stable metastin derivatives having excellent biological activities (a cancer metastasis suppressing activity, a cancer growth suppressing activity, a gonadotrophic hormone secretion stimulating activity, sex hormone secretion stimulating activity, etc.). By substituting the constituent amino acids of metastin with specific amino acids in the metastin derivative of the present invention, blood stability, solubility, etc. are more improved, gelation tendency is reduced, pharmacokinetics are also improved, and an excellent cancer metastasis suppressing activity or a cancer growth suppressing activity is exhibited. Furthermore, the metastin derivative of the present invention has the effects of suppressing gonadotropic hormone secretion, suppressing sex hormone secretion, etc.