This study investigated the ultrastructural changes in the adrenal gland in different stages of diabetes (onset, early, late) and the protective effects of curcumin. Seven groups of Wistar albino rats have six rats in each group. These were control, sham, curcumin, and four different Diabetes mellitus (DM) groups. For 14 days, the Sham group received corn oil, and the curcumin group received 30 mg/kg curcumin via intragastric gavage. DM group received a single dose of 50 mg/kg streptozotocin (STZ) I.P. for induction of diabetes. The DM-treated groups were given 30 mg/kg curcumin after seven days (DC1 group), after 21 days (DC2 group), and concurrently with STZ injection (DC3 group), respectively. Apoptotic processes in the adrenal gland were evaluated by immunohistochemistry. Stereological analyses showed that the cortex volume of DM and DC2 groups was significantly increased compared to the Cont group. An increased medulla volume was also observed in the DM and DC2 groups. Histopathological analysis showed numerous lipid droplets and increased cytoplasmic density of cells in the zona fasciculata in the DM group. The adrenal gland showed a healthy structure in the early curcumin treatment group (DC1). Findings indicate that curcumin administration exhibits a protective effect on the structure of the diabetic adrenal gland. However, a late curcumin treatment did not provide a sufficient protective effect. Compared to other groups, a strong expression of anti-caspase-3 in the cortex and medulla of the adrenal gland belonging to the DM group was found. Our results showed that giving curcumin at the beginning of diabetes ameliorates the adrenal gland.