BACKGROUND/AIMS: In this study, we analysed the changes of matrix metalloproteinase-9 (MMP-9) expression in the gastric antral epithelium in respect to H. pylori eradication. METHODS: Twenty patients with H. pylori-positive chronic gastritis or peptic ulcer were studied. The expression of MMP-9 in the gastric antral biopsy specimens were compared before and after H. pylori eradication using immunohistochemical study. The positive rates and intensity of MMP-9 staining were evaluated at surface mucous cells and pyloric gland cells. RESULTS: The positive rate of MMP-9 staining in antral mucosal epithelial cells of H. pylori chronic gastritis is 63.8%. The positive rates of MMP-9 staining in the surface mucous cells and pyloric gland cells were 75.5% and 52.0% before H. pylori eradication, respectively. On the contrary, the rates were 85.5% and 82.0% after eradication. The MMP-9 overexpression in the pyloric gland cells were noticeably increased after H. pylori eradication. Strong positive staining of MMP-9 was increased significantly after H. pylori eradication in the pyloric gland cells. CONCLUSIONS: These results suggest that MMP-9 over-expression is associated with H. pylori infection as a host inflammatory response. The increased expression after H. pylori eradication indicates that MMP-9 may have a important role in remodeling or early tissue repairing process of gastric mucosa.