We report a resected case of fetal adenocarcinoma. Fetal adenocarcinoma is a rare type of malignant lung tumor. A 53-year-old man had a 25 mm tumor in the right upper lobe on chest computed tomography. On fluorodeoxyglucose-positron emission tomography( FDG-PET), the tumor showed the accumulation of FDG with a standardized uptake value( SUV) max of 5.63. He underwent bronchoscopic examination, but a diagnosis was not established. We suspected that the tumor was primary lung cancer or metastatic lung tumor of rectal cancer which was resected prior to the treatment for pulmonary lesion. A right upper lobectomy with lymph node dissection was performed and the pathological diagnosis was high-grade fetal adenocarcinoma, stage IB (pT2aN0M0). The patient was treated with postoperative adjuvant chemotherapy. There has been no recurrence after surgery resection for 9 months.