Conscious sedation guided by bispectral index (BIS) during bronchoscopy has been proved to be a feasible approach. This study aimed to investigate the safety and efficacy of dexmedetomidine combined with midazolam for undergoing conscious sedation during bronchoscopy. The trial was registered prior to patient enrollment at the Chinese Clinical Trial Registry. Patients were randomized into DEX group (dexmedetomidine combined with midazolam) and FEN group (fentanyl combined with midazolam). Bronchoscopy was performed under awake sedation titrated to a BIS level of 60-80. The primary endpoint was the incidence of hypoxia, the secondary endpoint was the incidence of bradycardia and hypotension, effect of sedation including satisfaction degree (VAS) of the operators and patients and patients' willingness to undergo bronchoscopy again. A total of 222 cases in DEX group and 211 cases in FEN group completed the study. The incidence of hypoxia and tachycardia in DEX group was lower than that in FEN group (8.1% vs 14.7%, 10.4% vs 19.0%, p<0.05), and the incidence of hypotension and bradycardia in DEX group was higher than that in FEN group (6.8% vs 0, 15.3% vs 8.1%, p<0.05). Midazolam dosage was significantly lower in the DEX group than in the FEN group, and the duration of surgery was significantly longer in the DEX group. The differences in intraoperative discomfort of VAS score, satisfaction VAS score, and willingness rate to undergo bronchoscopy again were not statistically significant between the two groups. In addition, the proportion of "procedural interference by patient movement" in DEX group was higher than that in FEN group. The conscious sedation regimen of dexmedetomidine combined with midazolam monitored by BIS is considered to be safe and effective during bronchoscopy. The occurrence of hypoxia and tachycardia was less, and the fluctuation of blood pressure and heart rate was mild, but the proportion of bradycardia in dexmedetomidine group was higher than that in fentanyl combined with midazolam group.