Background and aim: Hydroalcoholic (70°) extract of leaves of Myrtus communis has been shown to have antidiabetic effect in streptozotocin induced diabetic rats in our previous study. In this study, we intended to determine the components of the mentioned extract and identify the mechanism for its action.Materials and Methods: The leaves of Myrtus communis were extracted using petroleum ether by soxhlet. 100 g of the powder remaining in the strainer soxhlet apparatus were placed in two different percolators. The extraction was carried out by percolation method with ethanol-water (1-1) or distilled water in 72 hours. The remaining powder of water extract was further extracted using again ethanol (percolation method). The study was conducted on forty-eight matured male Charles-River rats (200-300 g) divided into 6 groups (n=8). Diabetes mellitus was induced by single intraperitoneal injection of 35 mg/kg of streptozotocin (STZ). Hydroalcoholic, water, and ethanol extracts of Myrtus communis were used at the dose of 4, 2, and respectively 2 g/kg body weight per day for 5 days. All extracts were given orally by gastric tube.Results: We found that the total hydroalcoholic extract of Myrtus communis leaves showed a moderate antidiabetic effect. In this study, we showed that the ethanolic extract of leaves (2 g/kg) had a better hypoglycemic effect in diabetic rats compared with the aqueous extract (p < 0.05). Our results also showed that the oral administration of the ethanolic extract (2 g/kg) had an additive effect on the hypoglycemic action of glibenclamide (oral administration 5 mg/kg) in rats.Conclusion: A review of previous researches on leaves of Myrtus communis and also the present study suggests that the extracts may stimulate the β-cells of pancreas to release insulin.