A patient with fulminant idiopathic interstitial pneumonia was treated by sodium siverlestat and steroid pulse therapy following extracorporeal lung assist (ECLA). On arriving at the emergency room, Pa(O2) was 44.5 mmHg under oxygen with 10 l reserver mask, and emergency intubation was performed. X-ray showed honeycomb lungs, and strong fine crackle was audible. Sodium siverlestat (14 days) and steroid pulse therapy (3 days) were started. P/F ratio was 187, but decreased to 56 the next day. After ECLA for 3 days, P/F ratio decreased to 248. On day 29, X-ray showed much improvement, and the patient was weaned from ventilator. But on day 33, the patient deteriorated. And treatment with sodium siverlestat (14 days) and steroid pulse therapy (3 days) was performed again. The patient was weaned from ventilator again on day 66. Steroid pulse therapy was not effective shown by KL-6 of over 2000 IU l(-1), but sodium siverlestat was effective. We consider that sodium siverlestat is effective for fulminant idiopathic interstitial pneumonia.