Membranous nephropathy (MN) is a form of kidney disease that is idiopathic in 70%-80% of cases. Glomerular involvement in autoimmune thyroiditis can occur in 10%-30% of patients, and MN manifests in association with Hashimoto thyroiditis in up to 20% of the cases with glomerular involvement. Reports of MN associated with Graves' disease (GD) are extremely rare in the current literature. Herein, we report the case of a 46-year-old man admitted to the hospital with nephrotic syndrome and symptomatic hyperthyroidism due to GD. Kidney biopsy revealed a secondary MN pattern. Immunohistochemical staining for PLA2R was negative, and thyroglobulin showed weak and segmental staining along the glomerular capillary. Anti-thyroid peroxidase (TPO) antibody test was not performed. The patient was treated for GD with methimazole and prednisone, and despite reaching clinical improvement after 8 months, proteinuria remained close to nephrotic levels. In this scenario, the patient was submitted to radioactive iodine, and there was a dramatic reduction in proteinuria levels after treatment. In conclusion, GD association with MN is rare, and when present, diagnosis using PLA2R and immunohistochemistry can be useful in determining association. In addition, radioactive iodine therapy can be an effective treatment modality when preceded with immunosuppressive corticosteroid therapy.