Abstract Background and objective: Pectoral nNerve (PECS) block type-1 is an Ultrasound (US)-guided interfacial block that can be performed for postoperative analgesia management after breast surgery. In the procedure, a local anesthetic solution is injected into the interfacial area between the Pectoralis Major muscles (PMm) and Pectoralis minor muscles (Pmm). The present study compared PECS block type-1 administered preoperatively or postoperatively for postoperative analgesia after breast augmentation surgery. Methods: The patients were randomly divided into three groups (n = 30 in each): a preoperative PECS block group (Pregroup), postoperative PECS block group (Postgroup), and control group (Group C). Opioid consumption and Visual Analogue Scale (VAS) scores were evaluated at postoperative period. Results: The pains scores in the Pregroup were significantly lower than those in the control group. Although there was no significantly difference in the VAS scores of the Postgroup and control group at postoperative 1 hour, the scores in the Postgroup were significantly lower than those in the control group at all the other evaluated times (p < 0.05). The VAS scores in the Pregroup were significantly lower than those in the Postgroup 8 hours after the surgery. Opioid consumption was significantly lower in the Pregroup as compared with that in the other two groups (p < 0.05). The use of rescue analgesia in the Pregroup was significantly lower than that in the other groups (p < 0.05). Conclusion: Performing PECS block type-1 preoperatively reduced VAS scores and opioid consumption after breast augmentation.