OBJEC TIVE To expl ore the clinical significance of folic acid metabolic gene detection in methotrexate （MTX） treatment of acute myeloid leukemia （AML）. METHODS Therapeutic drug monitoring （TDM）pharmacists participated in the treatment process of an AML patient who had neurotoxic side effects such as dizziness ，headache，and vomiting after intrathecal injection of MTX. According to the results of the test of the folic acid metabolic gene MTHFR C677T（rs1801133）（mutant homozygous）and the results of MTX blood concentration monitoring （＜0.05 μmol/L），combined with clinical manifestations ，it was recommended to stop MTX ，give intravenous drip of calcium folinate for rescue ，and consider using azacytidine for follow-up treatment. RESULTS The doctor took the advice of TDM pharmacist ，and the above symptoms were significantly relieved after the patient rescued for 2 times and successfully discharged from the hospital. CONCLUSIONS For AML patients who meet the indications and receive intrathecal injection of MTX ，drug metabolism genetics testing and MTX drug concentration monitoring can be performed before medication ，which helps doctors and pharmacists evaluate the feasibility of drug treatment options and reduce medical risks.