We report a case of pneumonitis due to Rikkunshi-to. A 79-year-old woman was admitted to our hospital because of interstitial pneumonia. She complained of dry cough and dyspnea on exertion. Fine crepitations were heard on physical examination. The chest X-ray film revealed diffuse reticulonodular shadows in both lung fields. Under the suspicion of drug-induced pneumonitis, all drugs were stopped and she was given prednisolone. Consequently her complaints, laboratory data and chest X-ray findings markedly improved. Microscopic examination of transbronchial lung biopsy specimens showed interstitial pneumonia. The results of lymphocyte stimulation test and lymphocyte migration inhibition test were positive for Rikkunshi-to. Based on these findings, we diagnosed this case as pneumonitis due to Rikkunshi-to. To our knowledge, there has been no previous case of pulmonary hypersensitivity due to Rikkunshi-to reported in the world.