Objective To determine the effect of preventative infusion of low-dose dexmedetomidine (DEX) on the incidence of postoperative delirium among the elderly patients with a history of cerebral stroke. Methods Based on our previous random, double-blind, pracebo control study, a total of 161 elderly patients (≥65 years old) with a history of cerebral stroke who were admitted to the intensive care unit (ICU) of our hospital after surgery from May 2011 to November 2013 were enrolled in this study. They were randomly assigned into DEX group [an infusion of 0.1 μg/(kg·h) DEX, n=82] and placebo group (saline, n=79) in the morning from the second day after operation. Delirium was assessed twice daily with the Confusion Assessment Method for the ICU (CAM-ICU) within 7 d after surgery. Results The incidence of postoperative delirium was significantly lower in the DEX group than the placebo group [12/82 (14.6%) vs 23/79(29.1%), P=0.026]. After adjustment of confounding factors, multivariate logistic regression analysis showed that low-dose DEX infusion was an independent influencing factor for postoperative delirium (OR=0.36,5%CI:0.15-0.89, P=0.027). But the occurrence of hypotension was obviously higher in the DEX group than in the placebo group [42.7%(35/82) vs 24.1%(19/79), P=0.012], but no such difference was found between those who had the hypotension intervention from the 2 groups. Conclusion For the elderly patients with a history of cerebral stroke and transferred to ICU after surgery, postoperative prophylactic infusion of low-dose DEX could reduce the incidence of postoperative delirium, but hypotension should be monitored in the duration.