Gastric cancer is caused by the interaction of genetic and environmental factors. MicroRNA (miRNA) is involved in many cellular processes including proliferation, differentiation, and apoptosis and plays an important role in pathogenesis of gastric cancer, as demonstrated in many recent studies from perspectives including miRNA profiling, reciprocal modulation between epigenetic and miRNA, and Helicobacter pylori infection. MiRNA is highly stabe in blood, and therefore non-invasive diagnosis of gastric cancer using circulating miRNA may be promising.