A 63-year-old man was admitted to our hospital for acute heart failure. A chest CT scan revealed a large anterior mediastinal mass and pericardial effusion. Percutaneous needle biopsy showed that the mass was an advanced thymic cancer (squamous cell carcinoma). The patient was treated by combination chemotherapy of carboplatin and etoposide with concurrent radiotherapy (44 Gy). There was no severe toxicity except for grade 4 neutropenia. After 3 courses of chemotherapy, the mass showed an approximately 81% reduction in tumor size and disappearance of the pericardial effusion. Finally, the thymic cancer and small pulmonary metastatic lesions were all resected. This concurrent chemoradiotherapy can be effective against inoperable squamous cell carcinoma of the thymus.