Background:The most common cause of hyperthyroidism in areas without iodine deficiency is Graves' disease. There are reports of some hematological alterations in hyperthyroidism. This study was designed to measure the hematologic profile in the patients with Graves' disease before and after the treatment. Methods: In this cross-sectional study, 100 patients were selected with convenience sampling that diagnosed as autoimmune Graves' disease in our academic endocrinology clinic during 2014-2015. Inclusion criteria included autoimmune hyperthyroidism in patients who were referred to this center during the study period. Patients who refused to take part in the research, had recent infections disease, malignancies, surgical procedures, severe trauma, received immunosuppressive drugs or corticosteroids, high erythrocyte sedimentation rate (ESR) values during the last six months, and not responded to treatment with methimazole were excluded from the study. The simple sampling technique was used to select the patients. A complete blood count (CBC) was taken before and after treatment. The P-value less than 0.05 was considered as the statistical significance level. All data were analyzed using the Statistical Package for the Social Sciences 16.0 (SPSS Inc., Chicago, IL, USA) software. Results: One hundred patients with a mean age of 38 ± 9.8 years were included. There were no significant changes in the white blood cells (WBC) count, red blood cells (RBC) count, and platelets. Mild anemia (Hb=12.16±1.23) present before treating the hyperthyroidism that was significantly improved after treatment (P= 0.000). Conclusions: Our results showed that the only significant hematologic change in patients with Graves' disease was mild anemia that improves after treating the underlying thyroid disorder.