Objective: The study aims to investigate the effects of diabetes mellitus (DM) on ovarian injury and reserve in a rat model. Study Design: In this prospective experimental study, 16 female Sprague-Dawley albino rats (12 weeks, 220-240 g) were randomly divided into 2 groups. Group 1 included 8 normal healthy rats as controls. No drug was administered to the controls. Group 2 included the other 8 rats in which diabetes was induced by intraperitoneal injections of streptozotocin (STZ). After overt DM occurred (blood glucose >250 mg/dl), all the animals were euthanized and blood samples were collected by cardiac puncture for biochemical analysis. Bilateral oophorectomy was performed for histopathological examination. Immunoexpressions of nuclear factor-kappa B (NF-kB) and caspase-3 as well as anti-Müllerian hormone (AMH) levels were assessed. Values were analyzed by t test. Results: Immunoexpressions of NF-kB and caspase-3 were significantly higher in non-treated diabetic rats than in the control group (p = 0.011 and p = 0.010, respectively). In healthy control group, AMH levels (3.22 ± 0.58 ng/ml) were significantly higher than in the non-treated diabetic group (1.41 ± 0.25 ng/dl; p = 0.024). Conclusion: Hyperglycemia causes severe ovarian injury via NF-kB pathway and caspase-3 apoptotic pathway, leading to the decrease in ovarian reserve in STZ-induced diabetic rats.