A 56-year-old man with pure red cell aplasia (PRCA), hypogammaglobulinemia and mediastinal tumor was admitted to our hospital with of dyspnea, high fever and general fatigue. Chest X-ray showed a large cavity with a niveau in the left lung. Biopsy of the mediastinal tumor revealed an epithelial cell-type thymoma. Lung abscess with Good's syndrome and PRCA was diagnosed. Antibiotics was administered, and percutaneous catheter drainage of the lung abscess was performed. He recovered and was discharged. Hypogammaglobulinemia in the case may have resulted from reduced production of gammaglobulin associated with a quantitative B-cell defect.