Severe autoimmune hemolytic anemia was developed in the 45-year-old man whose anterior mediastinal growing mass, which was proved later as the invasive thymoma, had been found 4 years ago. The hemoglobin level was 6.2g/dl and both the direct and indirect Coombs' tests were positive. Prompt remission of the hemolytic anemia was achieved by thymectomy combined with corticosteroid therapy. Two months after the discontinuation of corticosteroid therapy his hemolytic anemia was recurred. The patient currently has been followed up for 8 months with no signs of local recurrence or hemolytic anemia and he is still receiving 15 mg of perdnisolone daily.