A 42-year-old female was admitted to our hospital because of continuous fever, anemia, and immature myeloid cells in peripheral blood. Bone marrow biopsy revealed severe myelofibrosis (MF). We performed computed tomography and identified several swollen mediastinal lymph nodes and nodules in the right upper lung. Lymph node biopsy showed an infection with Mycobacterium intracellulare (M. intracellulare), a nontuberculous mycobacterium (NTM). Antituberculosis drugs led to remission of the NTM infection. Bone marrow biopsy revealed marked improvement in MF and red blood cell infusion was not required after therapy. No prior cases of concomitant NTM with M. intracellulare and MF have been reported. This is thus the first reported case showing improvement of myelofibrosis after NTM treatment. This case report offers valuable insights into the pathology of MF.