Thymic undifferentiated carcinoma has a poor prognosis. We encountered a patient with thymic carcinoma associated with an intrathoracic disseminated lesion, who underwent surgery combined with intrathoracic hyperthermic perfusion after systemic chemotherapy and showed good results. The 45-year-old man was diagnosed as having a thymoma with an intrathoracic disseminated lesion. After he underwent three courses of systemic chemotherapy, he was admitted to our hospital. An anterior mediastinal tumor and an intrathoracic disseminated lesion remained, and were treated by surgical resection combined with intrathoracic hyperthermic perfusion. The tumors were histopathologically diagnosed as thymic undifferentiated carcinomas with pleural dissemination. At present, approximately 16 months after surgery, the patient is alive without recurrence.