Pure Red-Cell Aplasia [P.R.C.A.] is rare disease characterized by absence of erythroid precursors in the bone marrow, normocytic normochromic anemia with profound reticulocytopenia in the peripheral blood, and relatively or completely spared granulopoiesis and thrombopoiesis. The association rates of P.R.C.A. with Thymoma is approximately 50%, but only 5-10% of all patients with a Thymoma have a P.R.C.A.. P.R.C.A. is thought to be a variety of autoimmune disease, and humoral inhibitor, i.e. IgG, has been demonstrated experimentally. Its treatments such as thymectomy, immunosuppressants, steroid, androgenic hormone, and splenectomy have been tried but the result is not satisfactory and the prognosis is poor. We experienced a case of P.R.C.A. with Thymoma treated with thymectomy and postoperative steroid therapy, and which showed good postoperative recovery clinically and hematologically.