Hemophagocytic syndrome (HPS) is an uncommon hematological disorder that manifests as fever, splenomegaly, and jaundice, with hemophagocytosis in the bone marrow and other tissues pathologically. Secondary HPS is associated with malignancy and infection, especially viral infection. The prevalence of cytomegalovirus (CMV) infection in ulcerative colitis (UC) patients is approximately 16%. Nevertheless, HPS in UC superinfected by CMV is very rare. A 52-year-old female visited the hospital complaining of abdominal pain and hematochezia for 6 days. She was diagnosed with UC 3 years earlier and had been treated with sulfasalazine, but had stopped her medication 4 months earlier. On admission, her spleen was enlarged. The peripheral blood count revealed pancytopenia and bone marrow aspiration smears showed hemophagocytosis. Viral studies revealed CMV infection. She was treated successfully with ganciclovir. We report this case with a review of the related literature.