The effective control of blood glucose is the key to preventing or reversing diabetic complications. In this study, we examined the effects of Okchun-San (OCS), a Korean herbal medicine formula, on the blood glucose levels in diabetic C57BL/KsJ db/db mice. Herbal medicines were prepared from dried herbs by adding Coicis semen (OCS-C) or Oryzae semen (OCS-O). The experimental animals were divided into a control group and three sample groups; the sample groups received OCS-C (200 mg/kg), OCS-O (200 mg/kg), or acarbose (5 mg/kg) orally once a day for 12 days. On days 5 and 12, the fasting blood glucose levels of vehicle-treated db/db mice were significantly higher than day 0, while those of OCS-C, OCS-O, or acarbose-treated mice had not increased compared to the control group (p<0.01). During intraperitoneal glucose tolerance test (IPGTT), OCS-C group showed improved glucose sensitivity compared to the control group. These results suggest that OCS-C can be useful as an anti-diabetic therapy for Type 2 diabetic patients by lowering the blood glucose level.