PURPOSE: We aimed to investigate the predictive factors for early response to methimazole (MMI) in pediatric patients with Graves disease (GD). METHODS: Our study included 44 pediatric patients who were diagnosed with GD between January 1, 1993, and December 31, 2013, and were available for follow-up, achieving a normalization of thyroid functions (TFs) at the Chonbuk National University Hospital Pediatric Department. We retrospectively analyzed TFs such as tri-iodothyronine (T3), free thyroxine (fT4), thyroid-stimulating hormone (TSH), and thyroid antibody levels at diagnosis. We also examined their family history of thyroid disease, symptoms at presentation, and normalization time for TF after treatment. We divided our clinical series of patients into the following 4 age groups: <7 years old, 7-12 years old, 13-15 years old, and 16-18 years old. RESULTS: At diagnosis, the time of normalization of T3 was significantly shorter in the higher antimicrosomal antibody (AMA) group compared with the lower AMA group (2.53 months vs. 6.18 months) (P<0.05). However, the time of normalization of T3/fT4/TSH had no significant correlations with other variables such as age, sex, a family history of thyroid diseases, thyroglobulin, thyroid-stimulating immunoglobulin, or antithyroglobulin antibody (ATA). CONCLUSION: Higher serological titers of AMA at diagnosis may have prognostic value in the response to initial MMI treatment in pediatric hyperthyroid GD patients.