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Background: Propofol usually used for sedation for gastrointestinal endoscopy, result in short-term, reversible decline in cognitive function. This prospective cohort trial aimed to propofol plus dexmedetomidine can improve cognitive function for elective outpatient gastrointestinal endoscopy. Methods: Patients undergoing gastrointestinal endoscopy were included. Patients were randomized allocation into group C (groupC30 and groupC60), and group D. The group D was The group D was a continuous intravenous pumping of dexmedetomidine at a dose of 0.3μg/kg within 10min before anaesthesia; the group C were given an equal volume of normal saline instead. Patients underwent a MoCA test before sedation and at discharge. Results: The MoCA scores were similar at baseline in each group. Compared to baseline before gastrointestinal endoscopy, the MoCA scores were decreased each group ( group C30: p<0.001; group C60: p<0.001; group D: p=0.002). Compared to group C30, the MoCA scores were better in group C60 (p=0.03) and group D (p<0.001), and those in group D were higher than those in group C60 (p<0.001). Incidence of cognitive impairment in group C30 is 56.6% which ranks the highest among the three groups, and those in group D is 7.8% which ranks the lowest among the three groups, the difference is significant statistically (p<0.001). The MoCA scores were similar between the genders in each group (p>0.05). Conclusions: Dexmedetomidine added to sedation for gastrointestinal endoscopy can improve early cognitive function and reduce incidence of cognitive impairment.