Sustained-release compositions wherein a water-soluble physiologically active peptide is substantially uniformly dispersed in a microcapsule comprised of a lactic acid polymer or a salt thereof, and the physiologically active substance is contained in an amount of 15 to 35 wt/wt % to the total microcapsules and weight-average molecular weight (Mw) of the lactic acid polymer is about 11,000 to about 27,000, which is characterized by having a high content of the physiologically active substance, and suppression of the initial excessive release within one day after the administration and a stable drug sustained-release over a long period of time, and method for producing the same.