Background: Urtica dioica has been used in Iranian traditional medicine as a hypoglycemic agent. However there are reports with different results about the hypoglycemic activity of Urtica dioica.

Objective: This study was done to determine the chronic effect of Urtica dioica leaf extract in hyperglycemic Wistar rats.

Methods: 30 Wistar rats were allocated in groups of normal, hyperglycemic and treatment. Hyperglycemia in rats was induced by streptozotocin IP. Animals in treatment group received hydroalcholic extract of Urtica dioica (100 mg/kg/day) for 4 weeks intraperitoneally. The blood glucose was measured by using a Glucometer in 1st, 3rd and 5^th weeks. The animals in each group were sacrificed by ether anesthesia and pancreas β - cells in three groups were counted by histological examination.

Results: the Means±SE of blood glucose concentrations in diabetic group was significantly lower than treatment groups (253.8 ± 24.2 versa 356.2 ± 28.1 mg/dl). The percent of β-cells were 73.6%, 1.9% and 1.3% in normal, hyperglycemic and treatment groups, respectively.