Pure red cell aplasia (PRCA) is a rare cause of anemia associated with SLE. We herein report a case presenting with SLE and PRCA. A 33-year-old woman, who had been suffering from photosensitivity, proteinuria, and pancytopenia, was diagnosed to have SLE. She showed normochromatic normocytic anemia. The serum level of haptoglobin was <10 mg/dl, and Direct Coombs' test was negative. Her reticulocyte count was 0.8%. Her clinical and laboratory features, except for anemia, had recovered in response to 50 mg/day of prednisolone. The serum level of haptoglobin had normalized, but the reticulocyte count remained low. The bone marrow findings revealed erythroid hypoplasia, and she was diagnosed to have PRCA complicated with SLE. No viral DNA of human parvovirus B19 in her bone marrow was detected. The anemia gradually improved following the further use of 50 mg/day prednisolone. In order to disclose the mechanism of PRCA in this patient, we examined the effects of her peripheral T lymphocytes on erythrogenesis, using erythroid colony-forming cells (ECFC) in her peripheral blood. When we co-cultured peripheral T cells and ECFC, her T cells inhibited erythroid colony formation in a dose dependent manner. Several reports have shown the presence of inhibitory factors in SLE patients' serum such as antibodies against erythroid progenitors or erythropoietin, while other reports have shown abnormal T cells that inhibit the growth of erythroid progenitors. Our study suggests that these inhibitory T cells may therefore have played an important role in the pathogenesis of this patient.