Flexible bronchoscopy is more and more used for diagnosis and management of various pulmonary diseases in pediatrics. As poor coordination of children, the procedure is usually performed under general anesthesia with spontaneous or controlled ventilation to increase children and bronchoscopists' safety and comfort. Previous studies have reported that dexmedetomidine (DEX) could be safely and effectively used for flexible bronchoscopy in both adulate and children. However, there is no trial to evaluate the dose-finding of safety and efficacy of dexmedetomidine-remifentanil (DEX-RF) in children undergoing flexible bronchoscopy.The objective of this study is to evaluate the dose-finding of safety and efficacy of DEX-RF in children undergoing flexible bronchoscopy.One hundred thirty-five children undergoing flexible bronchoscopy with DEX-RF were divided into 3 groups: Group DR1 (n = 47, DEX infusion at 0.5 μg·kg for 10 minutes, then adjusted to 0.5-0.7 μg kg h; RF infusion at 0.5 μg kg for 2 minutes, then adjusted to 0.05-0.2 μg kg min), Group DR2 (n = 43, DEX infusion at 1 μg kg for 10 minutes, then adjusted to 0.5-0.7 μg kg h; RF infusion at 1 μg kg for 2 minutes, then adjusted to 0.05-0.2 μg kg min), Group DR3 (n = 45, DEX infusion at 1.5 μg kg for 10 minutes, then adjusted to 0.5-0.7 μg kg h; RF infusion at 1 μg kg for 2 minutes, then adjusted to 0.05-0.2 μg kg min). Ramsay sedation scale of the 3 groups was maintained 3. Anesthesia onset time, total number of intraoperative children movements, hemodynamics (heart rate, arterial pressure, pulse oxygen saturation (SpO2), respiratory rate), total cumulative dose of dexmedetomidine and remifentanil, the amount of midazolam and lidocaine, time to first dose of rescue midazolam and lidocaine, postoperative recovery time, adverse events, bronchoscopist satisfaction score were recorded.Anesthesia onset time was significantly shorter in DR3 group (14.23 ± 5.45 vs 14.45 ± 5.12 vs 11.13 ± 4.51 minutes, respectively, of DR1, DR2, DR3, P = 0.003). Additionally, the perioperative hemodynamic profile was more stable in group DR3 than that in the other 2 groups. Total number of children movements during flexible bronchoscopy was higher in DR1 group than the other 2 groups (46.81% 22/47 vs 34.88% 15/43 vs 17.78% 8/45, respectively, of DR1, DR2, DR3, P = 0.012). Total doses of rescue midazolam and lidocaine were significantly higher in DR1 and DR2 groups than that of DR3 group (P = 0.000). The time to first dose of rescue midazolam and lidocaine was significantly longer in DR3 group than DR1 and DR2 groups (P = 0.000). Total cumulative dose of dexmedetomidine was more in DR2 and DR3 groups (P = 0.000), while the amount of remifentanil was more in DR1 and DR2 groups (P = 0.000). The time to recovery for discharge from the PACU was significantly shorter in DR1 group compared with the other 2 groups (P = 0.000). Results from bronchoscopist satisfaction score showed significantly higher in DR2 and DR3 groups than that of DR1 group (P = 0.025). There were significant differences among the 3 groups in terms of the overall incidence of hypertension, tachycardia, hypoxemia, and cough (P < 0.05).Though it required longer recovery time, high dose of DEX-RF, which provided better stable hemodynamic profiles and bronchoscopist satisfaction score, less amount of rescue scheme, and children movements, could be safely and efficacy used in children undergoing flexible bronchoscopy.