SUMMARY Interstitial lung diseases (ILDs) are a diverse group of pulmonary disorders characterized by various patterns of inflammation and fibrosis in the interstitium of the lung. The underlying pathogenesis of ILDs is complex and associated with multiple rheumatologic conditions, such as systemic sclerosis, rheumatoid arthritis, pollymyositis and dermatomyositis, Sjögren’s syndrome, and systemic lupus erythematosus. As the disease progresses, excessive pulmonary fibrosis impairs alveolar gas exchange and damages pulmonary function. The common methods to diagnose ILDs, such as clinical manifestations, pulmonary function test, and radiological examinations are not specific for ILDs and not able to diagnose ILDs at the early stage due to their low sensitivity. So, the easy way is important to diagnose ILDs. One important biomarker for ILDs is the high-molecular-weight glycoprotein, Krebs von den Lungen-6(KL-6). KL-6 encoded by the MUC1 gene is a mucin-like glycoprotein with high molecular weight and expressed predominantly on the cell surface of type Ⅱ alveolar epithelial cells, and is detectable in the serum of patients with ILDs. We here report a case of ILDs associated with dermatomyositis and secondary Sjögren’s syndrome. A 60-year-old woman was admitted to our hospital with the chief complaints of debilitation, dry mouth, dyspnea and astasia. ILDs associated with dermatomyositis and secondary Sjögren’s syndrome was diagnosed clinically when the following criteria were satisfied: (1) development of dyspnea within 2 months of presentation, (2) pulmonary dispersion dysfunction, (3) bilateral infiltrative shadows on chest high resolution computed tomography (HRCT). She was treated with prednisone 50 mg/d prior to admission, but the result of therapy was not good. In our hospital she was treated with intravenous methylprednisolone and cyclophosphamide and oral hydroxychloroquine sulfate. Subsequently, her serum KL-6 levels gradually decreased after treatment, pulmonary diffuse function improved, and the improvement in the clinical manifestation and HRCT findings were observed. Nevertheless, the combination treatment of glucocorticoid and cyclophosphamide had contributed to the favourable outcomes. In conclusion, detection of serum KL-6 levels in ILDs associated with connective tissue diseases may be be-neficial to making a definitive diagnosis, predicting the prognosis and monitoring the disease activity, which would be of great help in clinical practice. However, a well-designed clinical study with more patients and a longer follow-up period are required to arrive at a more conclusive judgment on the role of serum KL-6 in patients with ILDs.