A case of grade Ⅱ myelosuppression caused by gefitinib in a patient of lung adenocarcinoma with EGFR genetic mutation was analyzed here to remind the clinical vigilance against possible risk of myelosuppression during the administration of gefitinib. Meanwhile, by reviewing relevant literature, we also discussed the possible adverse reactions caused by gefitinib and the treatments for myelosuppression, to provide reference for the safety of clinical medication.