A 57-year-old man admitted to our hospital with a pulmonary nodule detected by chest X-ray. Chest X-ray and chest computed tomography (CT) showed a solitary nodule with a spiculation in the right lower lobe (S8), 17 x 15 mm in size. His laboratory findings were almost within normal ranges. Positron emission tomography (PET) showed positive detection correspond to the nodule (SUV max: 5.76). Pathological diagnosis by CT-guided lung biopsy was suspected of gastrointestinal stromal tumor (GIST). Further examination of digestive organs revealed no abnormalities. The enlargement of the nodule was noted 2 weeks later, 23 x 18 mm in size. We couldn't rule out a malignant tumor and performed partial resection of the right lower lobe. Pathological diagnosis by intraoperative frozen section was "inflammatory myofibroblastic tumor (IMT), no malignancy". The patient is alive without any signs of recurrence for 4 months postoperatively.