Thymic large cell neuroendocrine carcinomas (LCNECs) are very rare. We here describe a case in which the tumor could be completely resected. A 55-year-old male was admitted to our hospital for treatment of an anterior mediastinal tumor found at a regular health check-up. The patient underwent an extended thymectomy of an invasive thymoma of Masaoka's stage II that had been suspected preoperatively. The tumor was located in the right lobe of the thymus and was completely resected. Final pathological diagnosis of the surgical specimen was thymic LCNEC. The patient underwent adjuvant chemotherapy with irinotecan and cisplatin in accordance with the diagnosis of a lung LCNEC, and is alive without recurrence or metastasis 16 months after surgery.