The present invention relates to a pharmaceutical composition for treating diabetes and its complications, containing a Quamoclit angulata extract, and more particularly to a Quamoclit angulata extract, a pharmaceutical composition for preventing or treating diabetes and its complications, a pharmaceutical composition for preventing or delaying aging, and a pharmaceutical composition for preventing or treating cancer, which contain the Quamoclit angulata extract. The compositions of the invention exhibit excellent effects on blood glucose lowering, promotion of insulin secretion, reduction of proteinuria, and reduction of lenticular opacity. Thus, the pharmaceutical compositions have excellent effects on the prevention or treatment of diabetes and its complications.