Objective: To explore the correlation of Narcotrend and observer’s assessment of alertness/sedation (OAA/S) scale in monitoring dexmedetomidine sedation. Methods: Sixty patients scheduled for elective lower limb surgery under combined spinal-epidural anesthesia were randomly divided into three groups, group D1 (n=20), group D2 (n=20) and group D3 (n=20). Patients in three groups were performed combined spinal and epidural anesthesia, and a bolus of dexmedetomidine was administered intravenously 15 min after spinal anesthesia. The initial dose in group D1, group D2 and group D3 was started from 0.8, 1.0 and 1.2 µg/kg, respectively. Pulse oxygen saturation (SpO2), heart rate (HR), mean arterial pressure (MAP), Narcotrend index and the corresponding OAA/S scale were recorded at 5-minute intervals until 30 minutes after administration. The cutoff values of Narcotrend index for OAA/S ≥3 and OAA/S ≤4 by receiver operating characteristic (ROC) curve and the correlation between Narcotrend and OAA/S scale by Spearman analysis were analyzed. Results: The calculated cutoff values for OAA/S ≥3 and OAA/S ≤4 by ROC curve were 45.50 (sensitivity of 0.87, specificity of 0.98, and area under the curve of 0.95) and 86.50 (sensitivity of 0.87, specificity of 0.93, and area under the curve of 0.96) for dexmedetomidine, respectively (P<0.05). The correlation coefficient between Narcotrend and OAA/S scale were 0.89 (P<0.05) by Spearman analysis. Conclusion: When dexmedetomidine reaches a suitable depth of sedation, the corresponding Narcotrend index was range between 46.50 and 86.50. The Narcotrend and OAA/S scale are well correlated, and the combination of them can provide different and complementary information better than using one of them alone.