Endoscopic submucosal dissection (ESD) is commonly performed as a treatment for gastric neoplasms. However, sedation with midazolam (MDZ) often does not reach satisfactory sedation levels during the procedure and the drug may suppress respiration and blood pressure. This study aimed to investigate the safety and efficacy of dexmedetomidine (DEX) with on-demand MDZ (the DEX group) in comparison with MDZ alone (the MDZ group) as a sedative during ESD of gastric neoplasms.