The effects of Maitake ( Grifola frondosa ) on blood glucose level in rats with streptozotocin-induced diabetes were investigated. Diabetic rats were produced by injecting 80mg/kg streptozotocin (STZ) into 2-day-old neonates. From the age of 9 weeks, the rats were given Maitake as a dietary admixture at 20% food weight for 180 days. Diabetic rats showed obvious diabetic symptoms such as hyperglycemia, hyperphagia, polydipsia, polyuria and glucosuria. The diabetic levels of blood glucose, water consumption, urine volume and glucosuria were significantly decreased in the rats fed Maitake. From these results, it may be considered that the bioactive substances present in Grifola frondosa ameliorate the symptoms of diabetes.