This study aimed to investigate the effects of curcumin treatment on ovaries at different periods of the diabetes disease. Fifty-six female Wistar albino rats (250-300 g) aged 12 weeks were divided into seven groups. No treatment was applied to the control group. The sham group was given 5 mL/kg of corn oil, and the curcumin group 30 mg/kg curcumin. In the diabetes mellitus (DM) groups, diabetes was induced by a single intraperitoneal dose of 50 mg/kg streptozotocin (STZ). The DM-treated groups received 30 mg/kg curcumin after either 7 days (DC1 group) or 21 days (DC2 group), or simultaneously with STZ injection (DC3 group). Number of follicles in the ovaries was estimated using stereological method. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), and superoxide dismutase (SOD) levels and catalase (CAT) activity were measured in serum specimens. We found that follicle number and volume of corpus luteum, blood vessel, and cortex, gonadosomatic index, and FSH and SOD levels all decreased significantly in diabetic ovaries, while relative weight loss, connective tissue volume, and CAT activity increased (p < 0.01). Curcumin treatment had a protective effect on the number of primordial follicles in the DC2 group and on antral follicle numbers in the DC3 group. Curcumin also exhibited positive effects on CAT activity and SOD levels, blood glucose levels, and corpus luteum, connective tissue, and blood vessel volumes in the DC2 and DC3 groups. Curcumin also ameliorated FSH levels in the DC1 and DC3 groups (p < 0.01). These findings suggest that curcumin exhibits protective effects on ovarian structures and folliculogenesis, especially when used concurrently with the development of diabetes or in later stages of the disease.