The gel composition according to the present invention comprises an amphiphilic block polymer that comprises a hydrophilic block chain having 20 or more sarcosine units and a hydrophobic block chain having 10 or more lactate units. The gel composition of the present invention has an excellent sustained releasability of a water-soluble drug, etc. and places a reduced burden on the living body. The gel composition may be provided in the form of an organogel, hydrogel or xerogel. A xerogel can be obtained by removing a dispersion medium from an organogel. A hydrogel can be obtained by wetting a xerogel with water or an aqueous solution.本發明的凝膠組成物含有兩親媒性嵌段聚合物，所述兩親媒性嵌段聚合物包含具有20個以上肌胺酸單元的親水性嵌段鏈、及具有10個以上乳酸單元的疏水性嵌段鏈。本發明的凝膠組成物的水溶性藥劑等的緩釋性優異、且對生物體的負擔少。凝膠組成物能以有機凝膠、水凝膠或乾凝膠的形態提供。藉由自有機凝膠除去分散介質而獲得乾凝膠，藉由利用水或水溶液使乾凝膠濕潤而獲得水凝膠。
