The purpose of this study was investigated the effects of YK-209 mulberry leaves on disaccharidase activites of small intestine and blood glucose-lowering in diabetic rats induced with streptozotocin (STZ). Male Sprague-Dawley rats weighing 100$pm$10 g were randomly assigned to one normal and four STZ-induced diabetic groups; YK-209 0% mulberry leaves diet (DM group),0.1% YK-209 mulberry loaves diet (DM-0.1Y group),0.2% YK-209mulberry leaves diet (DM -0.2Y group), and 0.4% YK-209 mulberry leaves diet (DM -0.4Y group). Diabetes was induced by intravenous injection of 55 mg/kg body weight of STZ in sodium citrate buffer (pH 4.3) via tail vein after 3 weeks feeding of experimental diets. Rats were sacrificed at the 9th day of diabetic states. The functional ingredients in the mulberry leaves, the 1-deoxynojirimycin (DNJ) contents of YK-209 mulberry leaves was higher than those of the Cheongil mulberry leaves. ${gamma}$ -Aminobutyric acid (GABA) and rutin contents of YK-209 mulberry leaves were 1.3 and 1.4 times higher than those of the Cheongil mulberry leaves, respectively, and vitamin C contents of YK-209 mulberry leaves were also higher than those of the Cheongil mulberry leaves. Intestine index was increased in all diabetic groups, compared with normal group but not significantly different among all diadetic groups. Level of blood glucose was decreased in diadetic rats by supplementation YK-209 mulberry leaves. The disaccharidase activities in proximal part of intestine such as maltase, sucrase, and lactase in YK-209 mulberry leaves supplementation groups were significantly lower than those of DM group, In conclusion, this research indicated that the functional ingredients of YK 209 mulberry leaves were higher than those of the Cheongil leaveses, and YK-209 mulberry leaves has the hypoglycemic effect in STZ-induced diabetic rats.