Purpose: The purpose was to assess the usefulness of midazolam in patients undergoing minor oral surgery under conscious sedation. Materials and methods: Bispectral index was examined in 20 patients receiving oral minor surgery with conscious sedation supplemented with local anesthesia. All patients included were ASA I and had no contraindications to the study medications. The patients were escorted to the day surgery operation room where, before the commencement of the sedation and surgical procedures, routine monitoring was applied, including the noninvasive monitoring of arterial blood pressure, arterial oxygen saturation, and 3-lead electrocardiogram (Electrocardiogram). Bispectral index electrodes were applied on the frontotemporal region after cleansing the skin with alcohol. Bispectral index was calculated with the Electrocardiogram monitor (A-2000; Aspect Co.). Midazolam was then titrated (initially 3mg wait 2min and 2mg). Vital sign and Bispectral index checked every 5 minute until the end of the procedure. The results were then compared. Results: The Bispectral index index values throughout the sedation study period alter many level. The index was dropped at 5 minutes after administration, but raised at injection and odontomy procedure. During the operation, mean Bispectral index index was higher than conscious sedation index range($60{sim}80$). The amnesic effect was shown 17 cases out of 20 cases(85%). Conclusion: Conscious sedation technique using midazolma is a safe and effective method of controlling behavior in oral and maxillofacial surgery.