A 81-year-old woman was referred to our hospital with pure red cell aplasia (PRCA) associated with a thymoma in May 2005. She had previously suffered from Evans syndrome which had been improved by prednisolone in 1999. She underwent a thymectomy, however her anemia subsequently got worse. Reticulocytopenia was noted and a marrow erythroid series was aplastic. Furthermore, both direct and indirect Coombs tests were positive, and the serum haptoglobin level was low. Based on these findings, the patient was diagnosed as having PRCA complicated with relapsed autoimmune hemolytic anemia (AIHA). The PRCA and AIHA were successfully treated with prednisolone and cyclosporine. To our knowledge, only one case of the PRCA complicated with AIHA after thymectomy has been reported. FoxP3 positive regulatory T-cells (Treg), which maintain immunological self-tolerance, were readily detectable in the excised thymoma. Thus, thymectomy resulted in removal of the Treg pool and might explain the autoimmune activation, believed to be one of the mechanisms of the post-thymectomy recurrence of the AIHA in this case.