Background <p>The serratus posterior superior intercostal plane block (SPSIPB) is a newly described truncal block. This study aimed to compare the effects of SPSIPB with conventional methods on postoperative opioid consumption and pain scores within 24&#xa0;h postoperatively.</p> Methods <p>This randomized controlled trial included 60 patients aged 18–65 years with an American Society of Anesthesiologists Physical Status of I–III. Patients were randomly assigned to either the SPSIPB or the control group. The primary outcome was cumulative opioid consumption within the first 24&#xa0;h postoperatively. Secondary outcomes included resting and dynamic Numerical Rating Scale (NRS) pain scores, Quality of Recovery (QoR)-15 questionnaire scores, intraoperative remifentanil consumption, and the incidence of postoperative nausea and vomiting.</p> Results <p>Total tramadol consumption was significantly lower in the SPSIPB group during the first 12&#xa0;h and at the end of the 24th hour postoperatively compared with the control group (<i>p</i> &lt; 0.05). The dynamic NRS score at 0&#xa0;h postoperatively was lower in the SPSIPB group (<i>p</i> = 0.001), whereas no significant differences in NRS scores were observed at other time-points. The postoperative QoR-15 scores were significantly higher in the SPSIPB group compared with the control group. Furthermore, the SPSIPB group had significantly lower intraoperative remifentanil consumption (<i>p</i> = 0.003). Nausea and vomiting were more frequent at 12 and 24&#xa0;h postoperatively in the control group compared with the SPSIPB group.</p> Conclusions <p>Serratus posterior superior intercostal plane block significantly reduced opioid use, and improved recovery quality after oncoplastic breast surgery.</p> Trial registration <p>NCT06225908, registered at ClinicalTrials.gov.</p>