Objective: To investigate the relationship between different sedation depth and the restlessness after using midazolam as an adjuvant during regional anesthesia. Methods: One hundred and fifty patients undergoing regional anesthesia were randomly divided into three groups. In group A, the patients were sedated at the level of OAA/S Ⅳ with midazolam during regional anesthesia. In group B and C, the sedation depths were kept at the levels of Ⅲ and Ⅱ respectively. The changes of BP, HR and SpO2 were recorded before and after midazolam.The rate of restlessness was also evaluated. Results: Blood pressures decreased in certain degree at 5 and 10 min after midazolam compared with those before in all three groups. BP decreased over 20﹪ of the baseline in 4 cases in group A, in 5 cases in group B, and in 5 cases in group C. There was no significant difference in BP dropping among three groups. Compared with group B and C SpO2 dropped significantly at 3 and 5 min after midazolam in group C, in which SpO2 was less than 93﹪ in 8 cases. The restlessness rate in group C was 22﹪, which was significantly higher than those in group A (2﹪ ,P＜0.01) and group B(4﹪ ,P＜0.05). Conclusion: The sedation depth is related to the rate of restlessness when midazolam is used as an adjuvant during regional anesthesia. It is suggested that the appropriate sedation depth for the patients under regional anesthesia is OAA/S Ⅲ.