Rationale: Mycobacterium fortuitum (M.fortuitum) is one of the rapidly growing nontuberculous mycobacterium (NTM) that is widespread in the environment. M.fortuitum can cause different types of disease including pulmonary disease, lymphadenitis, cutaneous disease, and disseminated disease. However, the infection presenting as septicemia is exceedingly rare. Patient concerns: A 48-year-old immunocompromised male with extranodal NK/T-cell lymphoma, nasal type was admitted to the hospital because of high fever for 10 days. Diagnoses: The pathogen identified twice in the hemoculture was M.fortuitum, but not in the sputum culture. The chest computed tomographic (CT) scan showed a chronic inflammatory infection. Interventions: The patient was treated with sulfamethoxazole and levofloxacin. Outcomes: The symptom of patient disappeared after the treatment for one week, and near-total absorption of the consolidation in CT after the treatment for one month. He continued the treatment for one year until the last negative hemoculture. Lessons: Although the M.fortuitum infection presenting as septicemia is rare, a high suspicion of M.fortuitum is required, particularly in the immunosuppressive patients. Timely and adequate treatment is necessary.