Objective To evaluate the efficacy and safety of PECS block under ultrasound guidance in multimodal analgesia after modified radical mastectomy.Methods Sixty female patients aged 18-65 years, ASA grade Ⅰ or Ⅱ, undergoing elective unilateral modified radical mastectomy were enrolled.Patients were randomly divided into PECS group (group P, n=30) or control group (group C, n=30).Two groups of patients were given flurbiprofen axetil 1 mg/kg via intravenous injection before operation.After general anesthesia induction, patients in group P received ultrasound guided pectoral nerves block with 30 ml of 0.375% ropivacaine.Patients in group C didn`t receive nerve block.Anesthesia maintenance was performed by combined intravenous-inhalation Anesthesia.Postoperative VAS pain scores (at 0, 3, 6, 12, and 24 postoperative hours), does of intraoperative remifentanil, rescue analgesic requirements in the first 24 h after surgery, adverse reactions were recorded.Results VAS score in group P was lower than that in group C at 0, 3, 6 and 12 h after surgery (P<0.05), there was no difference at 24 h.The dose of remifentanil and the rescue analgesic requirements in group P were lower than those in group C (P<0.05).There was no significant difference in postoperative adverse reactions between the two groups.Conclusion As a supplementary mode of multimodal analgesia, PECS block is a safe and reliable technique that provide better analgesia effect for modified radical mastectomy.