According to the guideline issued by the Japan Thyroid Association in 2006 for treatment of Graves' disease, discontinuing antithyroid drug (ATD) therapy is recommended when serum free thyroxine (FT4) and thyroid stimulating hormone (TSH) concentrations have been maintained within the reference range for a certain period after treatment with one ATD tablet every other day (minimum maintenance dose therapy, MMDT). In this retrospective study, the relationship between MMDT duration and remission rate was investigated. The participants were 107 consecutive patients with Graves' disease whose ATD therapy was stopped according to the guideline. Serum FT4, TSH, and TSH receptor antibody (TRAb) levels were measured when ATD was discontinued and every 3 months thereafter. The percentage of patients in remission was 86.9% at 6 months, 73.8% at 1 year, and 68.2% at 2 years after ATD discontinuation. The remission rate increased with MMDT duration, being significantly higher in patients with MMDT durations of 19 months or more than those with MMDT durations of 6 months or less. In patients with MMDT durations of 6 months or less, the remission rate was significantly lower in TRAb-positive patients than in TRAb-negative patients at the time of withdrawal of ATD; however, this was not observed in patients with MMDT durations of 7 months or more. These findings suggest that in patients who discontinue ATD after a certain MMDT duration, the remission rate increases as the MMDT duration increases, and ATD should not be discontinued in TRAb-positive patients with MMDT durations of 6 months or less.