A 71-year-old man with myelodysplastic syndrome (MDS) was admitted to our hospital because of recurrent high-grade fever. He was examined for bacterial and fungal infections and treated with antibiotics and antifungal agents. However, he did not achieve a definitive diagnosis and had no apparent improvement for more than a month. Bone marrow aspiration revealed transformation of MDS to acute myeloid leukemia and hemophagocytosis. In addition, Mycobacterium intracellulare was isolated from both a bone marrow specimen and a blood sample. Therefore, he was diagnosed with disseminated Mycobacterium avium complex (MAC) infection with hemophagocytosis. An antibody test was negative for human immunodeficiency virus (HIV). His general condition improved with anti-mycobacterial drug and steroid treatments. Clinicians should suspect disseminated nontuberculous mycobacterial infections in unexplained febrile patients with hematological disorders.