Myelodysplastic syndrome (MDS) with erythroid aplasia is a very rare disorder that has not been clearly defined. We experienced a case of pure red cell aplasia (PRCA), which evolved to MDS with erythroid aplasia. A 59-year-old male with transfusion-dependent PRCA was referred to our hospital for an evaluation of newly developed thrombocytopenia. Two years ago, PRCA was diagnosed by the laboratory findings and a bone marrow examination, which showed no evidence of any myelodysplastic features and thymoma. Upon admission, the bone marrow findings showed marked hypercellularity. with numerous dysplastic features in the three lineages including erythroid hypoplasia. These findings were compatible with a diagnosis of MDS with red cell aplasia. It is very interesting that the PRCA evolved to MDS with red cell aplasia, which strongly suggests an autoimmune mechanism for the development of MDS.