Objective To explore the relationship between microsatellite instability （MSI） and gastric cancer. Methods The related literatures at home and abroad were consulted and reviewed. Results The MSI is the replication errors caused by mismatch repair system defects. Gastric cancer which exhibiting MSI has characteris clinicopathological feature and prognosis. Detection the MSI of precancerous lesions and gastric cancer tissues can evaluate the risk and prognosis of gastric cancer. MSI include nuclear microsatellite stability （nMSI） and mitochondrial microsatellite instability （mtMSI）. Conclusions MSI plays an important role in the occurrence and development of gastric cancer. MSI may become a important indicator to forecast precancerosis risks and clinical prognosis of gastric cancer.