The present invention relates to a sustained-release formulation comprising a metastin derivative and a lactic acid-glycolic acid copolymer 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 release compound (I) or a salt thereof for a long time and exerts a medicinal effect of compound (1) or a salt thereof for a long time. Furthermore, the sustained-release formulation of the present invention, which improves patient's convenience by reducing the number of administration times, is an excellent formulation as a clinical medicine.
