The purpose of this study was to assess the sedative effects of four kinds of medication for management in the uncooperative 64 children aged from 18 to 92 months(ASA class I) and weighting between 10 and 32 kg. They were given randomly a dose of chloral hydrate 75mg/kg and hydroxyzine 25mg orally(group 1), midazolam 0.1mg/kg intramuscularly and $N_2O$(group 2), group 1 with additional $N_2O$(group 3) and group 1 with additional midazolam 0.5cc intranasally(group 4), respectively. According to rating scale, sleep, crying, movement and overall behavior were checked for evaluation of the clinical sedative effects. They were restraind with Pediwrap and were monitored by pulse oximeter for safety during treatment period. The results were as follows : 1. In the evaluation of sleep, rating scale of chloral hydrate and hydroyzine combination group was superior to midazolam and $N_2O$ combination group(p<0.001), but there was no significant difference between chloral hydrate, hydroxyzine and $N_2O$ combination group and chloral hydrate, hydroxyzine and midazolam combination group. 2. In the evaluation of crying, movement and overall behavior, there were significant differences between chloral hydrate and hydroxyzine combination group and midazolam and $N_2O$ combination group(p<0.05), but no significant difference between chloral hydrate, hydroxyzine and $N_2O$ combination group and chloral hydrate, hydroxyzine and midazolam combination group. 3. In the evaluation of overall behavior, the mean score of chloral hydrate and hydroyzine combination group was 2.94, midazolam and $N_2O$ combination group 2.07, chloral hydrate, hydroxyzine and $N_2O$ combination group 2.47 and chloral hydrate, hydroxyzine and midazolam combination group 2.24, respectively. 4. Evidence of adverse effect was not detected or reported during and/or after dental treatment.