We report a case of thymic basaloid carcinoma combined with multilocular thymic cyst (MTC). A 72-year-old man was found to have an abnormal shadow on a chest X-ray without pny symptoms. Chest computed tomography (CT) showed a smooth edged anterior mediastinum tumor projecting to the left lung field. After preoperative chemotherapy by irinotecan hydrochloride (CPT-11) and radiotherapy of 40 Gy, chest CT showed a large part of the tumor projecting to the left lung field had changed to a cyst. After the pericardium and upper lobe of the left lung to which the MTC adhered was partially resected via left thoracotomy, the tumor was resected with innominate vein via median sternotomy. The operation was followed by CPT-11 chemotherapy and radiotherapy of 20 Gy. The tumor was thymic basaloid carcinoma 3 x 2.5 x 2 cm in size combined with MTC 8.2 cm maximum in diameter. As he died of another disease 6 months after excision, sufficient postoperative observation was not obtained. Thymic basaloid carcinoma is rare and only 14 cases including the present case have been reported.