A 70-year-old male complained of pain in the left neck. A tumor of about 8 cm in diameter was detected by contrast CT in the region extending from the anterior to upper mediastinum. For definitive diagnosis, biopsy was performed under CT guidance, and the patient was diagnosed as having anaplastic carcinoma in the thymus (T4, N1, M0, stage IVb). Since surgical treatment was judged to be impossible because of infiltration into large blood vessels, the patient underwent chemotherapy by intra-arterial injection (CDDP, ADM) and radiotherapy (45 Gy), and obtained a CR. Metastasis to the spleen was detected during the follow-up period, but a CR was obtained by chemotherapy by intra-arterial injection (CDDP) and systemic chemotherapy (TXL). Generally, the prognosis for carcinoma in the thymus is poor, and the prognosis for anaplastic carcinoma in the thymus is considered especially poor. However, chemotherapy by intra-arterial injection of carcinostatics such as CDDP can be applied to patients in whom surgical treatment is impossible.