Herbal prescriptions have been recognized as potentially valid by the scientific medical establishment, and their use has been increasing. The present study investigated the antidiabetic effects of a new herbal formula (NHF) consisting of Polygonati Rhizoma, Rehmanniae Radix, Salviae Miltiorrhizae Radix, Puerariae Radix, Schizandrae Fructus, and Glycyrrhizae Radix. Streptozotocin-induced diabetic rats were orally administered NHF (300 mg/kg of body weight/day) for 4 weeks. The diabetic rats exhibited hyperglycemia, increased food and water intake, loss of body weight gain, elevated hepatic thiobarbituric acid-reactive substances (TBARS), and decreased activities of hepatic antioxidant enzymes (such as superoxide dismutase [SOD], catalase [CAT], and glutathione peroxidase [GSH-Px]), level of mRNA of glucose transporter (GLUT) 4 in soleus muscle, and numbers of insulin-positive cells and the size of $eta$-cells in pancreas. Administration of NHF significantly decreased the blood glucose level and the food and water intake and considerably increased the body weights of diabetic rats. Also, NHF treatment significantly increased plasma insulin levels and the number and size of insulin-immunoreactive cells in the pancreas of diabetic rats. Administration of NHF significantly lowered the levels of TBARS and increased the activities of SOD, CAT, and GSH-Px in the liver of diabetic rats. In addition, treatment with NHF increased the mRNA levels of GLUT4 in soleus muscle. Therefore NHF may be an effective preventive and therapeutic agent for diabetes mellitus.