In this case report, we present a 21-year-old girl having 45 days of fever, which did not respond to any of the antibiotics. Even the patient’s fever did not respond to intravenous acetaminophen. All efforts to find an infectious agent or malignancy were fruitless. Eventually, with suspicious to the macrophage activation syndrome (MAS), thus, bone marrow sampling was performed and the diagnosis was confirmed. In adult Still’s disease (ASD) patients who are treated with the appropriate medications, MAS should be considered in case of resistant fever and hemoglobin loss.