A 70-year-old man presented with a deteriorating fever and productive cough after the administration of drugs including L-carbocisteine against the common cold. Since chest radiograph revealed pulmonary infiltrates in the right lower lung field, he was admitted to our hospital, then L-carbocisteine was continued and antibiotics started. However, his symptoms, laboratory findings, and hypoxia worsened. Pulmonary infiltrates on his chest radiograph increased and chest CT demonstrated pulmonary consolidation with traction bronchiectasis and ground glass opacity with thickened of interlobular septae in the right lung field. Analysis of bronchoalveolar lavage fluid showed elevated numbers of total cells, neutrophils and eosinophils, and the CD4/CD8 ratio was 5.65. Under a suspected diagnosis of drug-induced pneumonia, we halted L-carbocisteine administration stopped and began corticosteroid therapy. Subsequently his symptoms and findings markedly improved. The drug lymphocyte stimulation test for L-carbocisteine using peripheral blood lymphocytes showed positive results. On the basis of the clinical course, laboratory and radiographic findings, we considered this case to possibly be drug-induced pneumonia due to L-carbocisteine. To our knowledge, this is possibly the first case of L-carbocisteine-induced pneumonia to be reported.