Taraxacum coreanum Nakai (TM) has been investigated for its antidiabetic activity in streptozotocin induced diabetic animals, but few studies have been conducted to evaluate its efficacy for treatment of type II diabetic mice. This study was designed to evaluate the efficacy of the water extracts of TM for the treatment of type II diabetes. Twenty four mice(C57BLKS/J Iar $-+Lepr^{db}/+Lepr^{db}$) with type II diabetes were randomly assigned either to a experimental group A (leaves extraction of TM), experimental group B(roots extraction of TM), experimental group C(leaves, roots and flowers extraction of TM) or control group. Water extracts of TM were ingested for 10 weeks. The changes of body weight, level of blood glucose, numerical change of insulin-immunoreactive cells and level of blood insulin were measured after treatment of water extracts of TM. A reduction of the blood glucose level after treatment of TM was observed in all the experimental groups. Especially, experimental C group showed significant reduction of blood glucose level compared with control group. Experimental C group induced an increase the level of blood insulin and density of insulin immunoreactive cells after treatment of TM. These results show that water extracts of TM can improve the severity in type II diabetic mice.