Obesity is an important public health problem worldwide. It increases the risk of many chronic diseases such as diabetes and cardiovascular diseases. Meanwhile, obesity is a major risk factor for several types of cancer including gastric cancer. Possible mechanisms linking obesity with gastric cancer may include obesity associated gastro-oesophageal reflux, insulin resistance, altered levels of adiponectin, leptin, ghrelin, and an abnormally increased blood level of insulin-like growth factor (IGF). Helicobacter pylori (H. pylori) infection is a well-recognized risk factor for peptic ulcer and gastric cancer. Recent studies have revealed an increased prevalence of H. pylori infection in obese patients, providing another clue for the increased incidence of gastric cancer in obese population. If this connection can be confirmed in animal models and a large cohort of patients, then eradicating H. pylori together with life style modification in obese individuals may help prevent the development of gastric cancer in the increasingly obese population.