Objective: Lysimachia genus has been recorded to be used in diabetes, traditionally and to have antidiabetic effect and antioxidant effects. The aim of this study was to evaluate the antidiabetic and antioxidant effects of aqueous extract of Lysimachia verticillaris (LV) and its isolated compounds, the percentage of apoptosis and histological changes in pancreatic beta-cells in rats with streptozotocin (STZ)-induced type 1 diabetes mellitus. Methods: Male Spraque Dawley rats were divided into 6 groups. STZ (40 mg/kg) induced diabetic rats were treated orally with aqueous extract (400 mg/kg) and isolated compounds (20 mg/kg). To interpret antidiabetic effect, serum glucose and insulin levels were measured and morphological changes of pancreas were examined. Serum samples were analysed for catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPX) levels to investigate antioxidant effect. The terminal deoxynucleotidyl transferase (TDT)-mediated dUTP-biotin nick end-labeling (TUNEL) assays were performed to reveal apoptosis of pancreatic beta-cells Results: Oral administration of the extract and isolated compounds reduced high blood glucose levels (p < 0.005). Morever, the treatments were resulted in increased serum insulin (p <= 0.05), CAT (p <= 0.05), SOD (p <= 0.05) and GPX (p <= 0.05). All applications with compounds, especially with quercetin 3-O-beta-glucopyranoside reduced the morphological impairment of pancreas. The percentage of TUNEL positive cells was higher (p <= 0.05) in the pancreatic islets of untreated diabetic group than others groups. Conclusion: According to results, the extract and isolated compounds of LV displayed antidiabetic effect, while quercetin 3-O-beta-glucopyranoside showed the highest antidiabetic effect. The antidiabetic effects of LV and phenolic compounds may be due to their antioxidant effects. Thus, LV and isolated compounds can be a potential source of herbal medicine for DM. However, it requires further investigations such as toxicological analysis studies and clinical trials.