After intravenous midazolam injection, the patients showed different response. Some of the children showed irritability or did not sedate with midazolam. We hypothesized that there might be genetric variations at the MDR1 or GABA2 according to response of midazolam. One hundred twenty eight pediatric patients were recruited. Midazolam (0.1 mg/kg) was injected intravenously before surgery. Sedation score (activity, vocalizations, emotional expressivity, state of apparent arousal) was checked before and 5 minutes after midazolam injection. After anesthesia, 2 ml of blood was sampled in 2 times and recorded the sampling time. Also other manifestations were recorded. Children were genotyped MDR1 and GABRA2. Haplotype was analyzed using the software package PHASE, version 2.0. The observed frequencies of MDR1 haplotype of TTT, TGC, CAC, CGC were 0.323, 0.208, 0.195 and 0.199, respectively. Those of GABRA2 haplotype of CCT, CT, GT were 0.211, 0.387 and 0.35, respectively. Twenty six patients were nonresponder who showed bigger sedation score after midazolam injection. Thirty nine patients showed smiling after midazolam injection.There was no significant difference in activity, vocalizations, emotional among MDR1 haplotype of TTT, TGC, CAC or CGC (P>0.05). However, there was a significant difference in activity, vocalizations (P<0.05). In conclusion, response of midazolam in children might be different with patients’ genotyping of GABRA2 but MDR1 is not related with response of midazolam.