Abstract: Objective: : To investigate the effect of Helicobacter pylori (H. pylori) on hMSH2 and hMLH1 gene expression in gastric carcinoma. Methods : The ultra-quick urease test was used to detect H. pylori in gastric carcinoma samples, corresponding adjacent mucosa and non-carcinoma gastric mucosa. Immunohistochemistry wasemployed to observe hMSH2 and hMLH1 expression. Results : The positive rate of hMSH2 protein in gastriccarcinoma tissues was significantly higher than that in carcinoma-adjacent mucosa and non-carcinoma mucosa(P<0.05), with no significant difference between the latter two groups(P>0.05). No statistical significancewas found in the positive rate of hMLH1 protein expression among gastric carcinoma tissues, carcinoma-adjacent mucosa and non-carcinoma mucosa(P>0.05). In the gastric carcinoma tissues, the positive rates ofhMSH2 protein and hMLH1 protein detection in those with H. pylori infection were significantly lower than inthose without H. pylori infection(P<0.05). In the carcinoma-adjacent mucosa, the positive rates of hMSH2 protein and hMLH1 protein in those with H. pylori infection were significantly lower than those without H. pylori infection(P<0.05). In the non-carcinoma mucosa, no significant difference was found in the positive rates ofhMSH2 protein and hMLH1 protein between those with and without H. pylori infection(P>0.05). Conclusion :Upregulation of hMSH2 protein and downregulation of hMLH1 protein may be potential markers for gastric carcinoma. Decreased hMSH2 and hMLH1 protein expression induced by H. pylori infection may promote gastriccarcinogenesis.