IEctopic pregnancy is a life threatening condition in the first trimester. Medical treatment with methotrexate can be administered in selected cases. Methotrexate (MTX) inhibits folate cycle in which 5,10-methylenetetrahydrofolatereductase (MTHFR) enzyme involved. Polymorphisms in the MTHFR enzyme gene is associated with changes in cellular composition of folates and may lead to toxicity of MTX. Herein we present a case report of successful treatment with single dose MTX in MTHFR mutant [C677T (rs1801133) and A1298C (rs1801131)] ectopic pregnant woman with extremely high serum beta fraction of human chorionic gonadotropin (β-hCG) levels with guidance of current literature. A 32 years old primary infertile patient was diagnosed as ectopic pregnancy with a β-hCG level of 18598 mIU/ml. Despite the extremely high levels of β-hCG, the decrease in β-hCG level was uneventful after only single dose MTX administration. She was followed up in outpatient clinical setting without any complication. To the best of our knowledge, This is the first case report in the literature describing a deal with MTX treatment and MTHFR mutancy in ectopic pregnancy treatment.