Invasive pulmonary aspergillosis (IPA) is a life-threatening complication of chronic granulomatous disease (CGD), a rare inherited disorder of phagocytes that is characterized by a defect in the production of reactive oxygen species (ROS) caused by mutations in NADPH oxidase 2. Here, we report a case of successful treatment of IPA complicated with CGD by the administration of interferon-γ (IFN-γ) in combination with voriconazole. The patient carried a splice site mutation in the CYBB gene, and the neutrophils could produce a certain amount of ROS. In this case, augmentation of ROS generation in the patient's neutrophils was observed after in vivo IFN-γ treatment, which may be attributable to the induction of a normal CYBB gene in the myeloid progenitor cells. This treatment, in combination with voriconazole, may have contributed to the reversal of IPA in this patient. These results suggest that the in vivo use of IFN-γ may augment ROS generation in CGD neutrophils, thus leading to the successful treatment of severe IPA.