Objective To evaluate the effects of different doses of dexmedetomidine administered intranasally on the median effective concentration (EC50) of sevoflurane inhibiting responses to laryngeal mask airway (LMA) insertion in the pediatric patients.Methods American Society of Anesthesiologists physical status Ⅰ or Ⅱ pediatric patients of both sexes, aged 1-3 yr, with body mass index of 20-25 kg/m2, scheduled for elective surgery under general anesthesia, were randomly divided into 3 groups: control group (group C) , dexmedetomidine 1 μg/kg group (group D1) , and dexmedetomidine 2 μg/kg group (group D2).In D1 and D2 groups, dexmedetomidine 1 and 2 μg/kg (in 1 ml of normal saline) were administered intranasally at 1 h before induction of anesthesia, respectively.Group C received the equal volume of normal saline administered intranasally.The children were separated from their parents at 45-60 min after intranasal administration and admitted to the operating room.The children inhaled 8％ sevoflurane until they lost consciousness.After loss of consciousness, the end-tidal concentration of sevoflurane was determined using the modified Dixon's up-and-down method.The initial end-tidal concentration of sevoflurane was set at 2％.The concentration was increased/decreased by 0.2％ in the next patient according to the response to LMA insertion.The patient's sedation status and with LMA acceptance were evaluated, and the patient's satisfaction with sedation and with LMA acceptance was recorded.Probit analysis was used to calculate the EC50 and 95％ confidence interval of sevoflurane inhibiting responses to LMA insertion.Results The patient's satisfaction with sedation and with LMA acceptance was significantly higher in D1 and D2 groups than in group C, and in group D2 than in group D1 (P＜0.05).The EC50 (95％ confidence interval) of sevoflurane inhibiting responses to LMA insertion was 2.03％ (1.91％-2.15％), 1.76％ (1.65％-1.87％) and 1.63％ (1.53％-1.73％) in C, D1 and D2 groups, respectively.The EC50 was significantly lower in D1 and D2 groups than in group C, and in group D2 than in group D1 (P＜0.05).Conclusion Dexmedetomidine 1 and 2 μg/kg administered intranasally can decrease the EC50 of sevoflurane inhibiting responses to LMA insertion in the pediatric patients, and 2 μg/kg produces better efficacy.