Objective: To study the effects of aqueous extract of Gmelina arborea bark on normoglycemic levels and streptozotocin (STZ) induced diabetes in rats. Methods: After single administration of the aqueous extract, plasma glucose level was determined up to 6 h. In subacute study, the aqueous extract was administered for 28 d and plasma glucose level was determined weekly. The diabetes was induced in rats by the intraperitoneal injection of STZ at a dose of 55 mg/kg body weight. The diabetic animals were divided into four groups containing six in each: Group 栺 diabetic control, Group 栻 and 栿 treated with the aqueous extract respectively at a dose of 250 and 500 mg/kg body weight once daily and Group 桇 treated with glibenclamide at a dose of 0.6 mg/kg body weight once daily. In acute study, the aqueous extract and glibenclamide were administered orally to rats. Plasma glucose levels were determined at 30, 60, 120, 240 and 360 min after the administration of the test samples. To study subacute effects, test samples (the aqueous extract and glibenclamide) were administered for 28 d consecutively. The effects of each test sample on plasma glucose level, body weight as well as food and water intake were also monitored weekly. The oral glucose tolerance test and biochemical indicators were estimated on day 28. Results: The aqueous extract did not significantly decrease the plasma glucose level in the normoglycemic rats as shown by the acute and subacute assays. However, after oral administration of the aqueous extract, the plasma glucose level was significantly ( P<0.001) decreased in the diabetic rats in the acute study. The long-term administration of the aqueous extract significantly ( P<0.001) reduced plasma glucose levels of the diabetic rats. Additionally, the aqueous extract also reduced loss of body weight and significantly decreased food and water intake in the diabetic animals. Nevertheless, no effects on biochemical indicators were observed at the selected doses. Conclusions: The aqueous extract of Gmelina arborea bark had antihyperglycemic activity against STZ induced diabetes in rats, after single and subacute oral administration. Moreover, it did not show significant glucose lowering effect in normoglycemic rats. Objective: To study the effects of aqueous extract of Gmelina arborea bark on normoglycemic levels and streptozotocin (STZ) induced diabetes in rats. Methods: After single administration of the aqueous extract, plasma glucose level was determined up to 6 h. In subacute study, the aqueous extract was administered for 28 days and the plasma glucose level was determined weekly. The diabetes was induced in rats by the intraperitoneal injection of STZ at a dose of 55 mg / kg body weight. The diabetic animals were divided into four groups containing six in Group: 栺 diabetic control, Group 栻 and 栿 treated with the aqueous extract respectively at a dose of 250 and 500 mg / kg body weight once daily and Group 桇 treated with glibenclamide at a dose of 0.6 mg / kg body weight once daily. In acute study, the aqueous extract and glibenclamide were administered orally to rats. Plasma glucose levels were determined at 30, 60, 120, 240 and 360 min after the administration of the test samples. To study subacute effects, test samples (the aqueous extract and glibenclamide) were administered for 28 d consecutively. The effects of each test sample on plasma glucose level, body weight as well as food and water intake were also monitored weekly. The oral glucose tolerance test and Biochemical indicators were estimated on day 28. Results: The aqueous extract did not significantly decrease the plasma glucose level in the normoglycemic rats as shown by the acute and subacute assays. However, after oral administration of the aqueous extract, the plasma glucose level was significantly (P <0.001) decreased in the diabetic rats in the acute study. The long-term administration of the aqueous extract significantly (P <0.001) reduced plasma glucose levels of the diabetic rats. and significantly decreased food and water intake in the diabetic animals. Nevertheless, no effects on biochemical indicators were observed at the selected d oses. Conclusions: The aqueous extract of Gmelina arborea bark had antihyperglycemic activity against STZ induced diabetes in rats, after single and subacute oral administration. Moreover, it did not show significant glucose lowering effect in normoglycemic rats.