Provided is a sustained-release preparation containing pioglitazone or a salt thereof as an active ingredient and showing superior sustainability. A sustained-release preparation containing pioglitazone or a salt thereof, which shows a dissolution ratio of pioglitazone of average 25-58% at the 2-hour time point, and average 60-100% at the 4-hour time point, in a dissolution test according to the 50 rpm USP Paddle Method and using pH 2.0 KCl/HCl buffer at 37℃ as a test solution.本發明提供一種緩釋性製劑，其含有吡格列酮(pioglitazone)或其鹽作為活性成份且展現優異之緩釋性。在根據50 rpm USP槳式模式(USP Paddle Method)及使用37℃之pH 2.0 KCl/HCl緩衝液作為試驗溶液之溶解試驗中，含有吡格列酮或其鹽之緩釋性製劑在2-小時的時間點展現吡格列酮溶解率為平均25至58%，及在4-小時的時間點為平均60至100%。
