Background: One of the major problems in pediatric surgery is anxiety and fear of separation from parents. Objectives: We studied the efficacy of different doses of oral midazolam for pre operation sedation of children. Patients and Methods:In this randomized, double-blinded clinical trial, 120 children aged 1 -8 years were enrolled in the study .The children were randomly assigned to one of 4 groups and received orally 0.5 mg/kg (group A), 0.8 mg/kg (group B), 1 mg/kg (group C), 0mg/kg (group D) of injectable midazolam mixed with 10 -15 mL apple juice 45 minutes before separation from parents. Sedation score, changes in MAP, HR, SPO2, respiratory rate, time of recovery and frequency of nightmares evaluated and analyzed with Kruskal-Wallis and ANOVA tests.