Hangeshashinto is an oriental medicine, usually prescribed for stomatitis in dentistry. Although drug-induced lung injury is a serious side effect of Oriental medicine, reports of injuries caused by hangeshasihnto are rare. We report a case of lung injury probably caused by hangeshashinto in a patient with chronic stomatitis. A 67-year-old woman visited a dental clinic with complaints of right buccal mucosa pain. Red lesions were present in the posterior region of the bilateral mandibular buccal gingiva and the surrounding buccal mucosa. Because gargling was ineffective, she was referred to our department. The lesions were diagnosed as chronic stomatitis by biopsy. We administered hangeshashinto, but the patient began to exhibit cough with small amounts of phlegm after 2 weeks. Additionally, exertional dyspnea gradually developed, and she visited a pulmonary medical clinic. Based on clinical examinations, blood tests, and chest CT findings, and the patient’s medical history, the diagnosis was lung injury probably caused by hangeshashinto. After hangeshashinto treatment was stopped, the patient’s symptoms improved after 1 week. The intraoral symptoms showed a tendency towards improvement, and the chest symptoms did not recur during 1 year 2 months of follow up. When hangeshashinto is prescribed, care must be taken regarding the possibility of serious side effects.