Reported here is a case of microsporidiasis that occurred in an acute myeloblastic leukemia (AML)-M3 patient who underwent chemotherapy. Fever, cough, expectorate and dyspnea were observed during the therapy. Since this case was considered as adult respiratory distress syndrome due to the chest X-ray and arterial blood gas findings, the male patient was bounded to a mechanical ventilator. As coagulation tests showed compatible findings with disseminate intravascular coagulation (DIC), it was thought to be a case of sepsis originating from the lungs and DIC. Pseudomonas aeruginosa and Staphylococcus aureus were found in the sputum of the patient. Although he was given combined antibiotic therapy, there was no reduction in the fever. A bronchoalveolar lavage (BAL) sample was taken and Microsporidia sp. was found upon staining with Giemsa. The patient died due to sepsis and DIC just before receiving therapy for microsporidiasis. Pulmonary infection with Microsporidia, although classically occurring in patients with HIV infection, may occur rarely in leukemia patients, especially if previously treated with systemic immune suppression. This case reinforces the need to consider Microsporidia as a possible pathogen in immunocompromised patients with pulmonary infections.