Abstract： Objective To investigate the sedative and analgesic effects of dexmedetomidine in serious patients. Methods Seventy-three patients admitted to the intensive care unit (ICU) from June 2009 to May 2010 were in need of sedation and analgesia. They were randomly divided into dexmedetomidine group (n=35) and midazolam group (n=38). Patients in dexmedetomidine group were given a loading dose (1μg/kg) for 10 minutes and then maintained with 0.2 - 0.7μg·kg-1·h-1. Patients in midazolam group were given a loading dose (0.06 mg/kg) and then maintained with 0.04 - 0.20 mg·kg-1·h-1. Pain symptom, length of mechanical ventilation, incidence of anterograde amnesia and awakening time, and changes in blood pressure (BP) and heart rate (HR) were compared between the two groups. Results There was no significant difference in gender proportion, age, or acute physiology and chronic health evaluation Ⅱ(APACHE Ⅱ) score between the two groups. The score of visual analog scale in dexmedetomidine group was lower than that in midazolam group (2.38±0.48 vs. 6.07 ±0. 79, P＜0.01)when intake dose was adjusted to maintain the Ramsay score of 2 - 4. The awakening time was shorter in dexmedetomidine group than that in midazolam group [(0.17 ± 0.03) hours vs. (1.63 ± 0.56) hours,P＜0.01]. BP was lowered in 2 patients with no significant change in respiration rate in dexmedetomidine group, while BP was lowered in 7 patients with reduced respiration rate in 2 patients in midazolam group (P＜0.05). All patients in midazolam group, in contrast with 4 patients in dexmedetomidine group, had anterograde amnesia (P＜0.05). There was no significant difference in length of machanical ventilation between dexmedetomidine group and midazolam group [(5.16 ± 1.68) hours vs. (5.21 ± 1.56) hours,P＞0.05]. Conclusion Dexmedetomidine is the recommended drug used for sedation and analgesia in ICU.