Objective To evaluate the efficacy of dexmedetomidine in preventing postoperative delirium in the patients with schizophrenia. Methods Ninety patients with schizophrenia of both sexes, with American Society of Anesthesiologists physical status Ⅰ or Ⅱ, aged 20-60 yr, weighing 45-90 kg, with a history of long-term use of antipsychotics, scheduled for elective emergency operation under general anesthesia, were divided into 3 groups (n=30 each) using a random number table method: high-dose dexmedetomidine group (group HD), low-dose dexmedetomidine group (group LD) and control group (group C). In HD and LD groups, dexmedetomidine was intravenously injected in doses of 1.0 and 0.5 μg/kg, respectively, over 10 min prior to induction of anesthesia, followed by continuous infusion at 0.4 and 0.2 μg·kg-1·h-1, respectively, until the end of operation.Anesthesia was maintained with propofol, remifentanil and sevoflurane, and bispectral index value was maintained at 40-55.Patient-controlled intravenous analgesia was performed within 48 h after operation, and visual analogue scale score was maintained≤3.The end-tidal concentration of sevoflurane (ETsev) was recorded at 30 min after endotracheal intubation.The sleep quality was evaluated and scored at 6 h and 1, 2 and 3 days after operation.The occurrence of delirium during emergency from anesthesia and within 3 days after operation was recorded.The occurrence of postoperative adverse reactions such as bradycardia, hypotension and hypoxemia was also recorded. Results Compared with group C, the ETsev, sleep quality scores at each time point after operation and incidence of delirium during emergency from anesthesia and within 3 days after operation (3%) were significantly decreased in group HD, and the ETsev, sleep quality scores at 6 h after operation and incidence of delirium during emergency from anesthesia were significantly decreased (P 0.05). The ETsev and incidence of delirium within 3 days after operation were significantly lower in group HD than in group LD (P 0.05). Conclusion Dexmedetomidine given as a loading dose of 1.0 μg/kg followed by a maintenance dose of 0.4 μg·kg-1·h-1 can prevent postoperative delirium effectively in the patients with schizophrenia. Key words: Dexmedetomidine; Delirium; Schizophrenia