BACKGROUND: Diabetes mellitus is one of the most common metabolic disorders with a severe impact on the quality of life. OBJECTIVES: The objective of the present study was to investigate the impact of the hydroalcoholic extract of Eryngos on blood glucose, blood cells, and pancreatic tissue. METHODS: Thirty-five male rats were prepared. After diabetes induction by streptozotocin, they were randomly divided into 5 groups, including; non-diabetic control, diabetic control, diabetic treated with hydroalcoholic extract of Eryngos at doses of 300 and 500 mg/kg administered intraperitoneally, and metformin at a dose of 500 mg/kg. At the end of the study, glucose level was measured, and blood cells and pancreatic tissue were examined. RESULTS: Hydroalcoholic extract of Eryngos caused a significant reduction in blood glucose. Given the adverse effects of diabetes on the number of WBC, Eryngos extract at a dose of 300 mg/kg had a protective effect on the number of WBC. It decreased their number significantly compared with the diabetic control group. This effect was the same for both diabetic and non-diabetic groups. Histopathological results also indicated that Eryngos extract significantly increased the number of islets of Langerhans and beta cells. CONCLUSIONS: The results suggest that the hydroalcoholic extract of Eryngos may be effective in the treatment of diabetes. Moreover, based on the biochemical and histological results, it can be concluded that the hypoglycemic effect of the extract is probably due to the restoration and repair of the islets of Langerhans