A 71-year-old man was admitted to the hospital because of general fatigue. There were few reticulocytes in the peripheral blood and no erythroblasts in the bone marrow. Chest CT revealed an anterior mediastinal tumor. Under a diagnosis of thymoma with PRCA, extended thymothymectomy was performed. Histological diagnosis was mixed type thymoma with no invasive growth beyond the capsule. Administration of predonisolone following surgery was not effective for PRCA. Otherwise, peripheral blood counts were significantly improved following occasional onset of acute bronchitis.