A 42-year-old started smoking heated tobacco in 20XX, and gradually increased its inhalation volume. At the end of February, he presented with fever and dyspnea. His saturation level was 90% by cannula at a flow rate of 3  L/min. CT revealed bilateral ground-glass opacities and infiltration of both lungs. He was hospitalized in another hospital and antibiotics were administered. His respiratory condition improved, but the radiological manifestations remained and he was referred to our department after three days for further examination. After admission to the former hospital, he had no history of any inhalation. A blood test showed an increase in the peripheral blood eosinophil count of 1,706/μL. In the bronchoalveolar lavage fluid, the lymphocyte and eosinophil percentages were 70% and 2%, respectively. Transbronchial lung biopsy showed lymphocyte-based inflammatory cell infiltration in the alveolar septum. From this clinical course, we diagnosed lung injury due to heated tobacco.