PurposeRemimazolam is a new type of ultra-short-effect intravenous anesthetic, that may provide adequate sedation for endoscopy while causing less cardiovascular or respiratory disturbance than propofol. The aim of this clinical study was to compare the efficacy and safety of two different doses of remimazolam with propofol for sedation during colonoscopy.Patients and methods225 subjects, aged 18 to 80 years, with American Society of Anesthesiology physical status I-III, were scheduled to undergo colonoscopy. All the subjects were randomly assigned to three groups, Low-Rem group (low dose remimazolam, 0.15 mg/kg, iv, n = 75), High-Rem group (high dose remimazolam, 0.2 mg/kg, iv, n = 75), and Propofol group (propofol 2 mg/kg, iv, n = 75). Every individual in this trial was given nalbuphine hydrochloride (0.2 mg/kg, iv) before administration of remimazolam or propofol. The primary outcome was the success rate of sedation. Haemodynamic parameters and adverse events were recorded to evaluate safety. Satisfaction of sedation from patients, anesthesiologists and gastroenterologists were also recorded.ResultsThe success rate of colonoscopy procedure was 100% in both High-Rem and Propofol groups, but it was 89% in Low-Rem group (p