In this study, the anti-inflammatory and antioxidant known as lycopene was applied to rats with experimental diabetes with the aim of investigating the detection of diabetes-related complications, and to determine the possible role of lycopene in diabetes complications regarding the effects of ACE activity. In order to induce diabetes in rats in the diabetes (D) and diabetes+lycopene (DL) groups, rats were given 45 mg/kg single-dose streptozotocin (STZ) intraperitoneally (i.p.); lycopene (10 mg/kg/day dissolved in sunflower oil) was administered to the rats in the lycopene-only (L) and DL groups. Blood glucose levels and HbA1c% in diabetes+lycopene group and diabetes group increased (p < 0.05) compared to control and only lycopene treated group. The highest level of ACE activity was observed in the (D) group (p < 0.05). Activity in the (L) group was also significantly greater than in the control group (p < 0.05). The (DL) group had lower (p < 0.05). ACE activity than the (D) group. Lycopene implementation was found to be effective in the inhibition of ACE activity, an important indicator of diabetes-related complications.