Tumors of the mediastinum are usually classified according to their location in the anterior, middle, or posterior mediastinum. Mediastinal teratomas are characteristically located at anterior mediastinum with only rare incidence in the posterior mediastinum. Two cases of posterior mediastinal teratoma were experienced recently, in the department of thoracic surgery, Seoul National University Hospital. The incidence of posterior mediastinal teratoma was 4.2% among 48 mediastinal teratomas in our experience. Two cases are all benign teratoma located at right posterior costophrenic angle, and histologically showed tissues from three germ layers including bone and fat.