AbstractBackground: Breast cancer is the world's most commoncancer among women, surgey is one of the main treatmentsfor this disease. Several ways to prevent post mastectomypain were used, one of them is the pectoral nerves blocks (PECs Blocks).Aim of Study: Study aimed to evaluate the efficacy ofultrasound guided Pectoral neves blocks for post-operativeanalgesia after modified radical mastectomy surgery.Patients and Methods: The study was carried out on fourtyadult female patients, who were scheduled for elective unilat-eral modified radical mastectomy, they were randomly assignedto two groups, Pectoral nerves block (Pecs) group, includedtwenty patients who received preoperative Pecs blocks (com-bination of Pecs I and Pecs II) followed by general anesthesia,and control group which included twenty patients who receivedgeneral anesthesia only.Results: It was found that VAS score was statisticallysignificant higher in control group than Pecs group. Therewas a significant difference concerning the total dose ofnalbuphine consumption in 24 hours post-operative betweenboth groups which is lower in Pecs group than in controlgroup. There was a higher satisfaction scores were obtainedin Pecs group than in control group with no detected compli-cations other than PONV.Conclusion: The Pecs blocks produce excellent analgesiawhen combined with general anesthesia for modified radicalmastectomy surgery. They are simple, easy-to-learn techniques,having easily identifiable landmarks based on good anatomicaland ultrasound knowledge, making them an excellent alterna-tive to the conventional thoracic paravertebral and neuroaxialblocks for breast surgeries. Also ultrasound guided Pecs blockssignificantly reduces VAS.