A 64-year-old man had been admitted to a previous hospital because of melena and a diagnosis of ulcerative colitis (UC, pancolitis type) had been made. He had received prednisolone and 5-ASA but steroid-induced hyperamylasemia had developed. Prednisolone had been tapered and halted, but it had resulted in UC relapse and thrombocytopenia. Then, he was referred to our hospital due to severe melena with hypovolemic shock. However, he was also positive for CMV antigen. Thus, we attempted to treat him with ganciclovir for CMV and intravenous cyclosporine (CsA) for UC. According to his clinical course, a reduction of CsA blood concentration induced leukocytopenia. Myelodysplastic syndrome (MDS, RAEB-1) was then revealed after bone marrow biopsy. A high blood CsA concentration may cause the improvement of UC and MDS conditions.