Ｏｂｊｅｃｔｉｖｅ　To determine the ED50 of intranasal dexmedetomidine(Dex) sedation for acceptance of mask inhalation anesthesia induction in children, and to compare the difference of ED50 among infants, preschool and school-age children.　Methods　ASA physical status Ⅰor Ⅱ children, scheduled for mask inhalation anesthesia induction, were allocated into 3 groups according to age: infant group(1-3 y), preschool group(4-6 y) and school-age group(7-12 y), and the case number expectation for each group is 35. Every child was titrated Dex into nostril 1 h before inhalational induction, and the initial dose of Dex was set at 2 μg/kg. Using the modified Dixon's up-and-down method depending on the sedation effect of the previous child, the dose of Dex in the next child was increased or decreased by 0.25 μg/kg. The tolerant degree of face mask was evaluated using a different 4?蛳point scale. 1-2 scores were considered as unsatisfactory and 3-4 scores were considered as satisfactory. Probit analysis was used for calculating ED50 and 95% confidence interval (CI) of intranasal Dex sedation.　Results　31, 28 and 30 cases were practically used in infant group, preschool group and school-age group, respectively. The ED50 of Dex for intranasal sedation was 1.94 μg/kg in infant group (95%CI: 1.72-2.18 μg/kg), 1.61 μg/kg in preschool group (95%CI: 1.41-1.82 μg/kg), and 1.30 μg/kg in school-age group (95%CI: 1.13-1.47 μg/kg), respectively. The ED50 among the three groups have significant difference(P<0.05).　Conclusions　The ED50 of Dex required for intranasal sedation before mask inhalation anesthesia induction is decreased followed by the increase of age in children.