We describe a 67-year-old man in who serum KL-6 levels were measured during drug-induced pneumonia. The patient was hospitalized, because of coughing, fever, and dyspnea on exertion after administration of Sho-saiko-to (herbal medicine). After he was hospitalized, his symptoms were relieved, and the infiltration shadow on chest X-ray films resolved, but after re-administration of Sho-saiko-to, fever and hypoxemia developed. The serum KL-6 level was again high one day after oral re-administration of the drug. However, the level of lactate dehydrogenase in serum was not high after the re-administration. After treatment with on oral steroid drug the serum KL-6 level decreased gradually, symptoms were relieved the previously high level of c-reactive protein in serum decreased, the previously high white blood cell count decreased, and radiographic findings returned to normal. The diagnosis of drug-induced pneumonia is difficult, because specific diagnostic measures have not been developed. In the present case the serum KL-6 level increased rapidly after re-administration of the drug, and therefore measurement of serum KL-6 level may be helpful in the diagnosis of drug-induced pneumonia.