Immune responses to Helicobacter pylori infection play important roles in gastroduodenal diseases. The contributions of tumor necrosis factor‐α (TNF‐α) and interferon‐7 (IFN‐γ) to the induction of gastric inflammation and to the protection from H. pylori infection were investigated using TNF‐α gene‐knockout (TNF‐α^−/−) mice and IFN‐γ gene‐knockout (IFN‐γ^−/−) mice. We first examined the colonizing ability of H. pylori strain CPY2052 in the stomach of C57BL/6 wild‐type and knockout mice. The number of H. pylori colonized in the stomach of IFN‐γ^−/− and TNF‐α^−/− mice was higher than that of wild‐type mice. These findings suggest that TNF‐α and IFN‐γ may play a protective role in H pylori infection. Furthermore, we examined the contribution of TNF‐α and IFN‐γ to gastric inflammation. The CPY2052‐infected TNF‐α^−/− mice showed a moderate infiltration of mononuclear cells in the lamina propria and erosions in the gastric epithelium as did wild‐type mice, whereas the CPY2052‐infected IFN‐γ^−/− mice showed no inflammatory findings even 6 months after infection. These results demonstrate that IFN‐γ may play an important role in gastric inflammation induced by H. pylori infection, whereas TNF‐α may not participate in the development of inflammatory response.