Background: Graves' disease (GD) is the most frequent cause of hyperthyroidism. There is debate about the role of vitamin D deficiency (VDD) in thyroid autoimmunity and the effect of vitamin D (VD) administration on thyroid autoimmunity. Objective: This work aimed to study if vitamin D insufficiency (VDI) in patients with GD was linked to elevated thyroid autoantibody titer levels and how vitamin D supplementation affects Thyrotropin receptor antibody (TRAb), anti-thyroid peroxidase antibody (TPO Ab), and Anti-thyroglobulin antibody (anti Tg) titers in patients who have both VDI or VDD and GD. Patients and Methods: A total of 30 patients with GD and 30 matched control individuals were involved in our study. Serum from these patients and controls was tested for vitamin D (25[OH]D) and thyroid profile. Following evaluation, patients (n=16) with GD and insufficient or deficient vitamin D were given cholecalciferol. An evaluation was conducted six months after the vitamin D treatment. Results: Cases with GD were associated with a higher prevalence of VDI than the control group (P<0.001). VD values in Graves cases revealed a negative association with both TRAb (P<0.001) and age (P<0.001). The results of multivariate regression analysis indicated that the most significant predictors of Graves were TRAb (P=0.002), anti-TPO (P=0.006) and VDD (P=0.013). Conclusion: Low VD level is linked to elevated TRAb titers in GD, and the level of thyroid autoantibodies were decreased after Vitamin D administration, pointing to a potential connection between elevated thyroid autoimmunity in GD patients and their vitamin D levels.