Rationale: Acquired pure red cell aplasia (PRCA) can be a secondary response to some autoimmune disorders. However, there is no data about the possibility of acquired PRCA being a secondary complication to ankylosing spondylitis (AS). Patient concerns: A 42-year-old male who had a history of AS for 14 years. He got serious anemia 17 months ago. Bone marrow smear indicated PRCA. Diagnose: He was diagnosed with acquired PRCA secondary to AS. Intervention: The combination treatment of immunosuppressants with hematopoiesis stimuli was successful. Outcomes: The patient recovered from PRCA, and showed improvement in his AS. Lessons: Acquired PRCA can be secondary to AS. Cyclosporine is effective in controlling AS arthritis syndrome and in addition to immunosuppressants, promotion of erythroid hematopoiesis is equally important.