Objective To study the expression of matrix metalloproteinase(MMP) in chronic obstructive pulmonary disease (COPD) and its clinical significance. Methods 36 Wistar rats were randomly divided into three groups : the normal group (A), the model group (B) and the medicine treatment group (C). Rats in group B and C were passively smoked for 75 days to establish COPD model. Group B were administered Vit A 15 mg/ kg before smoking. 75 days later,the rats were killed. Group A were killed 25 days after equal volume of saline was dripped in trachea. The pathological changes of lung tissue were observed in each group. The expression of MMP was determined by immunohistochemistry and ELISA. Result The enzymatic activity and the expression of MMP-2 and MMP-9 were reciprocally different as compared among the tree groups(P <0.01). Conclusion MMP expression is increased in impaired lung tissues of COPD rats.