Inflammatory myofibroblastic tumors (IMTs) of the lung are rare solid tumors and usually affect children and young adults. We describe an unusual form of an IMT of the left lower lobe invading the left atrium. A 9-year-old male patient with recurrent cough was referred for an evaluation of left-lung pneumonia. Transthoracic needle biopsy was performed, and the histopathological examination showed mixed inflammatory cells. Accordingly, an IMT was considered. Left lower lobectomy was performed. A portion of the tumor invading the left atrium was resected together with the intact atrial wall. The postoperative period was uneventful, and the patient was discharged on the sixth postoperative day.