A 54-year-old woman with advanced pancreatic cancer with peritoneal dissemination was given gemcitabine on days 1,8 and 15, and this was repeated on day 29 at a dose of 1,000-1, 150 mg/m2. After 5 courses,the total infusion was 20,900 mg. Thirteen days after the last infusion, she suffered from sudden dyspnea, and soon went into respiratory failure of WHO grade 4 with severe hypoxemia. Chest radiograph and CT showed interstitial infiltrates of bilateral lower lung. She was diagnosed with drug-induced interstitial pneumonitis due to gemcitabine. Corticosteroid therapy consisting of methylprednisolone (1 g/day) for three days followed by prednisolone(50 mg/day) was significantly effective in treatment of respiratory failure. Her symptoms were improved clinically within one week after the onset,and the interstitial shadows in the lungs had almost disappeared radiographically within three weeks after the onset. Respiratory symptoms did not appear again,but the patient died of progression of peritoneal dissemination of pancreatic cancer 73 days after the onset of the interstitial pneumonitis. Gemcitabine- induced interstitial pneumonitis is very rare, but could become a serious complication in long-term gemcitabine treatment.