Abstract: Objective To study the expression changes of cytokeratin-19 (CK-19) and its cleavage product CYFRA21-1 in the lung tissues of a rat acute pulmonary embolism (PE) model. Methods We constructed a rat acute PE model and collected the samples of bronchoalveolar lavage fluid (BALF). The mRNA level changes of CK-19 were identified by semi-quantitative RT-PCR, and the protein level changes of it were validated by western blot methods. The immunohistochemical method was employed to study the distribution and expression changes of CK-19 in the lung tissues after PE. The serum and BALF concentrations of CYFRA21-1 were determined by RIA methods. The saturation of arterial blood oxygen (SaO2) was evaluated. Results The mRNA and protein expression levels of CK-19 decreased gradually after acute PE. CK-19 was expressed mainly in the bronchial epithelia and alveolar epithelia and down-regulated obviously. The serum and BALF concentrations of CYFRA21-1 increased obviously compared with controls and the levels of SaO2 had an obvious decreasing trend. Conclusion The acute PE not only reduced the expression of CK-19 but also enhanced its catabolism. So the determination of its fragment CYFRA21-1 can play an important role in the judgment of severity and prognosis of acute PE.