Acute interstitial pneumonia (AIP) is a rare fulminant form of lung injury that presents acutely; usually in a previously healthy individual. It corresponds to a subset of cases of idiopathic adult respiratory distress syndrome (ARDS). Invasive pulmonary aspergillosis is a disease occuring predominantly with defects in immunity such as hematologic malignancy, influenza infection, postchemotherapy, long-term corticosteroid treatment. Invasive aspergillosis has worse prognosis and most cases are diagnosed at postmortem autopsies. We experienced a case of acute interstitial pneumonia with an invasive aspergillosis during corticosteroid treatment. Acute interstitial pneumonia with invasive aspergillosis was diagnosed by an open lung biopsy using thoracoscopy, showing fungal hyphae with sepsis and an acute angle branching invasion of the lung tissue and blood vessels. The patient was treated with IV amphotericin-B, but died due to septic shock.