A 64-year-old man who ingested liquid paraffin as a laxative for over two years, was admitted to our hospital with a persistent interstitial lung shadow and marked elevation of serum KL-6. He had no overt symptoms although his chest radiograph revealed ground glass opacities in the left lower lung field and right middle and lower lung fields. We performed fiberoptic bronchoscopy. Exogenous lipoid pneumonia was diagnosed based on microscopic analysis of the bronchoalveolar lavage fluid that revealed the presence of lipid-laden alveolar macrophages. We instructed the patient to discontinue liquid paraffin ingestion and observed his clinical course. The chest radiograph and thoracic computed tomography revealed a tendency to improve and serum KL-6 decreased with time. Serum KL-6 may be an important index of the severity of exogenous lipoid pneumonia.