Interleukin-33 (IL-33) is a novel cytokine involved in diabetes mellitus (DM) but its role in diabetic ovarian injury is unknown. As IL-33 is modulated by apoptosis, we aimed at investigating the effect of diabetes on ovaries in terms of evaluating apoptosis and IL-33 in a rat model. In this prospective experimental study, 16 female, nonpregnant Sprague–Dawley albino rats (12 weeks, 220–240 g) were randomly divided into two groups. Group 1 included eight healthy nondiabetic rats as controls and group 2 included eight rats in which diabetes was induced by intraperitoneal (i.p) injection of streptozotocin (STZ). After overt DM occurred (blood glucose >400 mgr/dl), all animals were euthanized and blood samples were collected by cardiac puncture for biochemical analysis. Bilateral oophorectomy was performed for histopathological examination. Serum levels of IL-33 and ovarian IL-33 and caspase-3 immunoexpressions were assessed. Immunoexpressions of caspase-3 and IL-33 were significantly higher in ovarian stromal cells of the diabetic rats compared to the controls. Also, in diabetic group, serum IL33 levels were significantly higher than the control group. In conclusion, increased IL-33 was observed both in serum and ovaries of STZ-induced diabetic rats as well as increased apoptosis in these diabetic rats. IL-33 may contribute to the apoptosis in diabetic ovarian injury.