Objective:To compare the sedative and analgesic effect and safety of dexmedetomidine at different doses combined with lidocaine with intravenous administration after modified radical mastectomy for breast cancer. Methods:Sixty ASAⅠ-Ⅱpatients aged from 18 to 65 years with body weight index of 18-30 kg·m-2 were treated by modified radical mastectomy. The patients were randomly divided into 3 groups:lidocaine group (group L, n=20), low dosage dexmedetomidine and lidocaine group (group D1, n=20) and high dosage dexmedetomidine and lidocaine group (group D2, n=20). Group L was intravenously given lidocaine 1. 5 mg·kg-1 before the operation and intravenously infused lidocaine 1. 5 mg·kg-1 ·h-1 during the whole operation process. Group D1 was intravenously infused dexme-detomidine 0. 3μg·kg-1 in 10min before the operation, and intravenously infused lidocaine 1. 5 mg·kg-1 ·h-1 during the whole opera-tion process. Group D2 was intravenously infused dexmedetomidine 0. 6 μg·kg-1 in 10min before the operation, and intravenously in-fused lidocaine 1. 5 mg·kg-1 ·h-1 during the whole operation process. The propofol Ce was recorded when the modified OAA/S reached 3 (Ce3) and BIS reached 80 (Ce80) during the up period, the VAS in the 1st, 6th and 24th hour after the surgery (VAS1-24), and nausea and vomiting in the first postoperative day were also recorded and observed. Results:No difference was found in the demographic data among the 3 groups with modified OAA/S of 3 (Ce3) and BIS of 80 (Ce80). VAS of group D1 and D2 was significantly decreased when compared with group L in the 1st postoperative hour(P<0. 05). In the 6th and 24th postoperative hour, VAS of group D2 was much lower than that of group L and D1(P<0. 05), however, no difference was found between group L and D1. There was no significant difference in the propofol Ce during the up period and the adverse reactions in the 1st postoperative day among the 3 groups. Conclusion:Dexmedetomidine at the dosage of 0. 6 μg·kg-1 combined with lidocaine can significantly reduce the pain and optimize the short-term prognosis after modified radical mastectomy.