Mucoepidermoid carcinoma of the thymus is a rare carcinoma and there is little agreement about the treatment of this tumor. According to the analysis of previously reported tumors, biologic behavior of the tumor correlated with the spread of the lesion and degree of differentiation. We report a case of this tumor in a 31-year-old man. Resection of the tumor included the left upper lobe of the lung, the phrenic nerve, pericardium and disseminations in the pleura. The clinicopathological feature of this case was high-stage disease and low-grade histology. Postoperative chemotherapy and radiotherapy were performed, and the patient is alive without recurrence 14 months after surgery.