Helicobacter pylori is a primary etiological agent leading to chronic gastritis and peptic ulcer. The organism is also associated with gastric cancer in epidemiological studies. However detailed mechanism of carcinogenesis remains unknown. Histolopathological studies indicate that chronic H. pylori infection progresses over decades through stages of chronic gastritis, atrophy, intestinal metaplasia, dysplasia and cancer. Gastric atrophy and intestinal metaplasia are considered as precancerous lesions, but whether H. pylori eradication improves these lesions and prevents metachronous gastric cancer is controversial. And the issue has not been evaluated in gastric cancer patients. However, despite the conflicting evidences from two open labelled randomized controlled trials, current guidelines from various regions recommend H. pylori eradication treatment in patients who were treated for gastric cancer by surgically or endoscopically. Thus, it is important to evaluate whether H. pylori eradication can improve known precancerous lesion, i.e. glandular atrophy and intestinal metaplasia in gastric cancer patients. Such histological improvement can eventually reduce secondary gastric cancer development and provide evidence for current guidelines.