Abstract Purpose To investigate the effect of dexmedetomidine on intraoperative blood glucose hemostasis in elderly patients undergoing non-cardiac major surgery. Methods This was secondary analysis of a randomized controlled trial. Patients in dexmedetomidine group received a loading dose dexmedetomidine (0.6 μg/kg in 10 min before anaesthesia induction) followed by a continuous infusion (0.5 μg/kg/hr) till 1 h before the end of surgery. Patients in control group received volume-matched normal saline at the same time interval. Primary outcome was the incidence of intraoperative hyperglycemia (blood glucose higher than 10 mmol/L). Results 303 patients in dexmedetomidine group and 306 patients in control group were analysed. The incidence of intraoperative hyperglycemia showed no statistical significance between dexmedetomidine group and control group (27.4% vs. 22.5%, RR = 1.22, 95%CI 0.92–1.60, P = 0.167). Median value of glycemic variation in dexmedetomidine group (2.5, IQR 1.4–3.7, mmol) was slightly lower than that in control group (2.6, IQR 1.5–4.0, mmol), P = 0.034. In multivariable logistic analysis, history of diabetes (OR 3.007, 95%CI 1.826–4.950, P < 0.001), higher baseline blood glucose (OR 1.353, 95%CI 1.174–1.560, P < 0.001) and prolonged surgery time (OR 1.197, 95%CI 1.083–1.324, P < 0.001) were independent risk factors of hyperglycaemia. Conclusions Dexmedetomidine presented no effect on intraoperative hyperglycemia in elderly patients undergoing major non-cardiac surgery. Trial registration Present study was registered at Chinese Clinical Trial Registry on December 1, 2015 ( www.chictr.org.cn , registration number ChiCTR-IPR-15007654).