Abstract: Objective To investigate the expression and significance of Krebs von den Lungen-6(KL-6) mucin in rats with pulmonary fibrosis induced by paraquat poisoning. Methods Seventy male SD rats were randomly divided into four groups:paraquat poisoning 1,4,7,14,21 and 28 d group and normal saline control group.1 ml paraquat aqueous solution with the concentration of 20% was diluted with sterile isotonic saline into 100 ml,and the poisoning group was administered intraperitoneally with 18 mg/kg,the control group was given the same amount of saline intraperitoneal injection.The rats with intraperitoneal injection of drugs that did not meet the modeling standards and died were excluded,after 1,4,7,14,21 and 28 d injection,6 rats were killed in the poisoned group respectively,and 6 rats were killed in the control group,respectively.The pathological changes of lung tissue were observed.The changes of lung tissue fibrosis were observed by Masson staining.The level of KL-6 in serum was detected by enzyme-linked immunosorbent assay(ELISA) in the expression of KL-6. Results The level of KL-6 in serum of normal control group was about 11.42 ng/ml,the level of KL-6 protein in the serum of 4,7,14 and 21 d group gradually increased and was higher than that in the normal control group(P<0.05),and decreased after 21 days while they were higher than the control group.The expression of KL-6 in the lung tissue of 1,4,7,14 and 21 was significantly higher than that in the normal control group(P<0.05),and decreased after 21 days,but they were always higher than the control group. Conclusion KL-6 changes with the degree of pulmonary fibrosis in paraquat poisoning,which may be involved in the process of pulmonary fibrosis in paraquat poisoning rats.