Objective: In this study, the levels of essential trace elements, namely copper (Cu), iron (Fe), manganese (Mn), selenium (Se), and zinc (Zn), in the lung, kidney, brain, and testicular tissues of diabetic rats induced by streptozotocin (STZ) were compared, and the effect of melatonin on these levels was evaluated. Materials and methods: 40 male Sprague-Dawley rats were divided into four equal groups: control group (CONT), diabetes group (DM), melatonin group (MEL), and diabetes+melatonin group (DM+MEL). The control group was fed with standard rat feed and received no added treatment. The rats in the DM and DM+MEL groups were injected with STZ at a single dose of 60 mg/kg intraperitoneally (i.p.). The healthy animals in the DM+MEL group were given a 10 mg/kg/day dosage of melatonin (i.p.) for 6 weeks. The levels of trace elements in the lung, brain, kidney, and testicular tissues of the rats were evaluated by using inductively coupled plasma optical emission spectrophotometer (ICP-OES). Results: The Cu levels were found to have significantly increased in the kidney and testicular tissues of the rats in the DM and DM+MEL groups compared to the CONT group (p < 0.05). Zn and Fe levels were found to have significantly increased in the DM, MEL, and DM+MEL groups in the lung, kidney, and testicular tissues (p < 0.05). Mn levels were observed to have significantly increased in the kidney tissue in the DM+MEL group when compared with the CONT group. There was no significant difference in Se levels between the groups in any of the tissues (p > 0.05). Conclusion: As a result, it was observed that trace element levels in tissues affect diabetes, and melatonin application significantly increases trace element levels. It is thought that using melatonin as a supplement will decrease tissue damage in diseases with systemic effects such as diabetes.