We encountered two patients with clinically diagnosed idiopathic interstitial pneumonia with acute respiratory distress syndrome (ARDS). Both patients required mechanical ventilation within 24 hours after admission. We managed these patients using lower tidal volume ventilation (tidal volume: 5-6 ml/kg), antibiotics, sivelestat sodium hydrate and steroid pulse therapy followed by oral prednisolone therapy. Respiratory failure was relieved within 2 weeks following treatment There was no four-fold rise in screen viral titers and screening investigations of autoantibodies were negative. Based on these findings, we diagnosed these cases as having acute interstitial pneumonia (AIP). AIP represents a small subset of patients with ARDS without any associated or predisposing factor. Sivelestat sodium hydrate is an anti-neutrophil elastase inhibitor and is used for the treatment of acute lung injury (ALI)/acute respiratory distress syndrome (ARDS). Therefore, sivelestat sodium hydrate may be one of the treatment options for acute respiratory failure due to idiopathic interstitial pneumonia.