A 52 year-old Japanese male was admitted to our hospital because of fever during steroid and immunosuppressive-drug therapy for unclassifiable vasculitis. A blood examination at admission showed pancytopenia. We did a bone marrow puncture and diagnosed him as low-grade myelodysplastic syndrome. He was treated with broad antibiotics and granulocyte colony-stimulating factor for febrile neutropenia. But his respiratory condition worsened, and follow-up chest CT findings revealed diffuse granular shadows and ground-glass attenuation. We added his therapy with antifungal drugs and antiviral drugs, but his condition deteriorated. The pathological findings of bone marrow showed epithelioid cell granuloma, consistent with mycobacterial infection. We suspected him as milliary tuberculosis and started antituberculosis therapy, which improved his respiratory condition. Mycobacterium culture of bone marrow aspirate and blood were positive, and Mycobacterium kansasii was identified. From the above, we diagnosed him as disseminated M. kansasii infection. The risk factors of disseminated M. kansasii infection in our case are hematological disorder and immunosuppressive therapy. Disseminated M. kansasii infection can expect the effect of therapy, so we should try to identify the bacteria.