Objective To observe the effect of ropivacaine combined with dexmedetomidine in serratus anterior plane block on postoperative analgesia in patients undergoing breast cancer surgery.Methods Ninety patients scheduled for modified radical mastectomy in this hospital from May to October 2023 were divided in-to three groups by using random number table method:the R0.375 group,the DR0.375 group and the R0.500 group,with 30 cases in each group.All the three groups received serratus anterior plane block before surgery.The R0.375 group was injected with 20 mL of 0.375%ropivacaine,the DR0.375 group with 20 mL of a mix-ture of 0.375%ropivacaine and 1.0 μg/kg dexmedetomidine,and the R0.500 group with 20 mL of 0.500%ropivacaine.All patients received opioid-based patient-controlled intravenous analgesia pump after surgery.The numerical rating scale(NRS)was used to assess resting and movement pain at 1,2,6,12 and 24 hours postoperatively,and the pain-time area under the curve(AUC)was calculated.Postoperative opioid consump-tion,time of first analgesic drugs use were recoreded;sedation status at 1 hour postoperatively was evaluated by the American society of anesthesiologists(ASA)grading,quality of life at 24 hours postoperatively was as-sessed by the 15-item quality of recovery(QoR-15)scale,and postoperative adverse reactions were recorded.Results Compared with the R0.375 group,AUC of the resting pain-time and movement pain-time and the opioid consumption at 12 and 24 hours postoperatively of the DR0.375 group and the R0.500 groups were re-duced(P<0.05),while QoR-15 score after surgery was increased(P<0.05).The time of first analgesic drugs use in the R0.500 group was significantly longer than that in the R0.375 group(P<0.05).At one hour after surgery,all the three groups were evaluated as having mild to moderate sedation,with no statistical-ly significant differences among groups(P>0.05).There were also no statistically significant differences in the incidence of postoperative adverse reactions among the three groups(P>0.05).Conclusion Dexmedeto-midine can significantly improve the analgesic effect of low-concentration ropivacaine in serratus anterior plane block and reduce postoperative opioid consumption.