Oblective To define the median effective dose (ED50) and 95%effective dose of fentanyl for inhibition of emergence agitation after sevoflurane-remifentanil anesthesia in children.Methods Twenty six ASA ⅠorⅡchildren aged 5-8 yr weighing 15-30 kg undergoing adenoidectomy under general anesthesia were studied.The patients were unpremedicated.Anesthesia was induced with inhalation of 8%sevoflurane (fresh gas flow=6 L/min)and iv remifentanil 1μg/kg.The patients were mechanically ventilated after tracheal intubation.Fentanyl was injected iv to inhibit emergence agitation.The dose of fentanyl was determined by using modified Dixon's upand-down method (increment or decrement of 0.5μg/kg).The initial dose of fentanyl was 4 μg/kg.Anesthesia Sevoflurane inhalation and remifentanil infusion were terminated at the end of operation.The patients were transferred to the PACU.No alteration in the ventilatory settings was made.Stimulation of the patients was avoided during emergence.The emergence time and the occurrence of agitation,nausea and vomiting and respiratory depression within 4h after operation were recorded.ED50,ED95 and 95%confidence interval (CI) of fentanyl for inhibition of emergence agitation were calculated.Results ED50 was 3.01μg/kg (95%CI 2.52-3.40μg/kg) and ED95 3.81μg/kg(95%CI 3.41-6.22μg/kg).No nsusea and vomiting and respiratory depression occurred within 4h after operation.The emergence time was (11.3±2.6) min.Conclusion The ED50 and ED95 of fentanyl for inhibition of emergence agitation after sevoflurane-remifentanyl anesthesia were 3.01 and 3.81μg/kg respectively in children.