The incidence of cystic lesions of anterior mediastinum is low, which is responsible for approximately 10% of anterior mediastinal tumors. We presented a special case of primary anterior mediastinal tumor with both prominent cystic change and extreme high carbohydrate antigen 19-9 level of cystic fluid here. From the finding of this case report, we suggested that the diagnosis of cystic anterior mediastinal tumors should include both cystic seminoma and mature cystic teratoma.