To examine the mRNA expression of matrix metalloproteinase 9 (MMP-9) and the gelatinase activity of its inhibitor, tissue inhibitor of matrix metalloproteinase 1 (TIMP-1) in the primary epithelial cells of patients with COPD, airway epithelial cells were taken from 15 COPD patients and cultured in vitro. The patients were divided into three groups, COPD group, normal smoking control group and non-smoking control group, with 5 subjects in each group, on basis of the smoking history and lung function. The semi-qualitative RT-PCR was employed to determine the mRNA levels of MMP 9 and TIMP-1 and SDS PAGE was used for the determination of the gelatinase activity of MMP-9 and TIMP-1. Our result showed that the mRNA of MMP-9 and TIMP-1 in epithelial cells of the non-smoking subjects was at a low level The mRNA of MMP 9 and TIMP-1 in COPD patients and smokers was significantly higher than that in non-smokers (P＜0.05). No significant difference was found in the levels of MMP-9 and TIMP-1 in epithelial cells between the COPD patients and smokers. The MMP-9/TIMP-1 ratios in COPD patients and smokers were significantly lower than that of non-smokers (P＜0.05). The gelatinase activity in the epithelial cells of both COPD patients and normal smokers was increased (P＜0.05), but no difference existed in the gelatinase activity in the epithelial cells between COPD patients and normal smokers. It is concluded that the transcription of MMP-9 and TIMP-1 and the gelatinase activity of MMP-9 and MMP-2 in the epithelial cells in COPD patients were increased, which resulted in an imbalance of MMP-9/TIMP-1, thereby causing pulmonary fibrosis. These factors play important roles in the pathogenesis of COPD.