A 41-year-old female presented at our hospital with fever and joint pain. She was diagnosed with influenza A and was administered oseltamivir. Next day, she started to cough at the same time as her fever subsided. Seven days later, she revisited our hospital because her cough had worsened. Chest CT revealed diffuse ground-glass opacities with lower lobe predominance, suggesting influenza pneumonia or drug-induced lung injury caused by oseltamivir. However, influenza pneumonia was excluded, leaving drug-induced lung injury as the most probable cause, based on the course of the fever and the cough that appeared after fever had resolved. The bronchoalveolar lavage fluid lymphocyte count was elevated and histological examination of a transbronchial lung biopsy specimen revealed mild alveolitis. These findings were consistent with drug-induced lung injury. CT findings of ground-glass opacities improved without any treatment. Based on the above, we concluded that drug-induced lung injury due to oseltamivir treatment was the most probable cause of the patient's presentation.