Present invention is to provide a sustained-release composition which contains a physiologically active substance in high content even when gelatin is not included, and suppresses its initial excessive release and, thus, can achieve a stable release rate over about one month. A sustained-release composition containing a lactic acid-glycolic acid polymer having a ratio or weight average molecular weight and number average molecular weight of about 1.90 or lower, or a salt thereof, and a physiologically active substance.