The presence of anti-gastric parietal cell antibodies (AGPAs) has been strongly associated with the pathogenesis of pernicious anemia and atrophic gastritis and has been rarely reported in thyrotoxicosis. In addition, AGPAs more commonly occur in the Western population. No case of AGPA occurring in thyrotoxicosis has been reported in Korea to date. We report a case involving the occurrence of AGPAs in a thyrotoxicosis patient examined at the Hanyang University Hospital. Upon medical consultation, a 55-yr-old woman with no significant medical history was found to have elevated levels of cholesterol, AST, ALT, gamma glutamyl transferase, and mild anemia. Further blood tests revealed elevated levels of T3, free T4, and thyroid-stimulating immunoglobulin (TSI), low level of thyroid-stimulating hormone (TSH), and negative results for the anti-thyroid peroxidase antibody (anti-TPO) and anti-thyroglobulin antibody (anti-TG), for which the patient was diagnosed with thyrotoxicosis. To rule out autoimmune hepatitis in the explanation of the continuously elevated levels of AST and ALT, the autoimmune target (AIT), anti-smooth muscle antibody (ASMA), anti-liver/kidney/microsomal antibody (LKM), anti-mitochondria antibody (AMA) and anti-neutrophil cytoplasmic antibody (ANCA) tests were done, and the results were all negative. However, during this process, the patient tested positive for AGPA, when stomach tissue was used as the sample. Finally, the patient was diagnosed with thyrotoxicosis without any other autoimmune disease. This is the first report of confirmed presence of AGPA in a thyrotoxicosis-only patient in Korea.