The present invention relates to a sustained release formulation comprising a metastin derivative and a lactic polymer having a weight average molecular weight of about 5,000 to about 40,000 or a salt thereof. The sustained release formulation of the present invention slowly and stably releases compound (I) or a salt thereof over a long period of time and exerts medicinal effects of compound (I) or a salt thereof over a long period of time. Furthermore, the sustained release formulation of the present invention which improves patient"s convenience by reducing frequency of administration, is an excellent formulation as a clinical medicine.
