Many types of regional nerve blocks have been used during anesthesia for modified radical mastectomy. In recent years, the use of pectoral nerve (PECS) block has gained importance in postoperative analgesia, but there are still controversies regarding its efficacy. There is especially no consensus on the optimal type of PECS block to be used. Herein, we attempt to evaluate the analgesic efficacy of the PECS block after radical mastectomy.We searched PubMed, EMBASE, and the Cochrane library for randomized controlled trials (RCTs) for studies regarding PECS versus general anesthesia (GA) that were published prior to May 31, 2018. Outcome measures such as intra- and postoperative consumption of opioids, postoperative nausea and vomiting (PONV), need for postoperative rescue analgesia, and pain scores were analyzed. After quality evaluation and data extraction, a meta-analysis was performed using Review Manager 5.3 software, and the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system was used for rating the quality of evidence.A total of 8 RCTs and 2 cohort studies involving 993 patients were eligible. Compared with the GA group, the PECS block group effectively reduced the intraoperative and postoperative use of opioid drugs, incidence of PONV, need for postoperative rescue analgesia, and pain scores within 0 to 6 hours after surgery. However, subgroup analysis showed that PECS I block did not have a significant advantage in reducing the intra- and postoperative consumption of opioids. Results for each outcome indicator were confirmed as having a high or moderate level of evidence.Even considering the limitations (evaluations of efficacy in different age groups and for chronic pain were not carried out) of this meta-analysis, it can be concluded that the PECS II block is an effective anesthetic regimen in modified radical mastectomy that can effectively reduce the intra- and postoperative consumption of opioids, postoperative PONV, and the need for postoperative rescue analgesia and can alleviate early pain (0-6 hours) after surgery.