Epigenetic alterations, represented byaberrant DNA methylation, are present in gastrointestinal cancers. Detection of cancer- specific DNA methylation can be used to detect cancer, and detection of colon cancer-specific aberrant DNA methylation is alreadyapproved byFDA. Aberrant DNA methylation is potentlyinduced bychronic inflammation, and also is accumulated in normal tissues before a cancer develops. In gastric cancer, potential of cancer risk diagnosis bymeasurement of aberrant DNA methylation in normal gastric mucosae has been clinically demonstrated. Therapeutically, DNA demethylating agents have been alreadyapproved for hematological tumors byFDA, and promising results in clinical trials against gastrointestinal cancers have been reported. Also, histone deacetylase inhibitors have been already approved for hematological tumors, and clinical trials against gastrointestinal cancers have been reported. Selection of right dose, schedule, combination, and patients is the keyto future success.