Pleural effusion as one of the most common manifestations of pulmonary diseases is a rare symptom of anterior mediastinal teratoma that might mislead general physicians. In this study we report a rare case of pleural effusion and anterior mediastinal teratoma accompanying each other. The patient was a 21-year-old woman who suffered from dyspnea, cough, fever and manifestations of pleural effusion were obvious in chest X Ray (CXR). Computed tomography scan showed a cystic mass with lipid component. After thoracotomy, a mass was taken out from medial lobe of right lung and the results of pathology showed the mature mediastinal teratoma. The patient remained well with no evidence of recurrence on follow-up CXRs 6 months after the surgery.