Abstract: Abstract:Objective To investigate the effects and the minimal effective concentrations of ropivacaine combined with fentanyl on the patient's controlled epidural analgesia (PCEA) after breast cancer operation. Methods Seventy-five ASA (American statistical association)Ⅰ~Ⅲ patients of breast cancer undergoing operations were randomly divided into three groups (n=25 in each group). Ropivacaine in different concentration combined with fentanyl was used in each group. Group Ⅰ：0.1% ropivacaine +3 μg/ml fentanyl+0.10 mg/ml mizalamine+0.10 mg/ml tropisetrone; Group Ⅱ：0.125% ropivacaine+3 μg/ml fentanyl+0.10 mg/ml mizalamine+0.10 mg/ml tropisetrone; Group Ⅲ：0.15% ropivacaine +3 μg/ml fentanyl+0.10 mg/ml mizalamine+0.10 mg/ml tropisetrone+ 0.9%N·S to 100 ml. All patients received patient-controlled epidural analgesia(PCEA). Heart rate, mean artery pressure, respiration rate, and SpO2 were monitored at 6, 12, 24 and 48h after analgesia. VAS,Ramesay score,Bromage greade, sedative score，satisfaction of analgesia and side effects were also recorded. Results Average VAS score in group Ⅰ,Ⅱ and Ⅲ was all below 3.There were significant difference in heart rate, mean atery pressure, respiration rate at 6,12,24 and 48h（P<0.05). There were significant difference in VAS,Bromage,Ramesay at different time point（P<0.05). There were no significant difference in three groups (Pvas=0.154, Pramesay=0.470),while there were significant difference in groupⅢcompared to groupⅠ,Ⅱ in Bromage(P＝0.013, P<0.05). Conclusion Different concentrations of ropivacaine combined with fentanyl provide the optimum balance between pain relief and side effects in postoperative radical mastectomy of breast cancer, 0.10% ropivacaine combined with fentanyl might be lower in the rate of complication and which should be the minimal effective concentration.