Bronchogenic cysts are generally presented as a well defined mass that have thin and smooth wall in the intrapulmonary or mediastinal area by simple chest radiographs. We present the case of a 20-year-old man with a ill-defined left upper lobe mass, found by chest radiographs. At the preoperative examinations, chest computed tomography showed ill-defined mass with Hounsfield Number 26, and nonspecific findings were shown by the bronchoscopy and percutaneous needle aspiration. The patient was undertaken the left upper lobectomy. The surgical specimen contained a ill-defined mass, measuring 2×3 cm. On the section of the mass, a cyst containing dark brown thick materials was noted. The cyst was unilocular, and the wall showed a trabeculation. Microscopically, the cystic mass was lined with ciliated pseudostratified columnar epitheliums and surrounded by smooth muscle and cartilage.