Background: The thoracodorsal artery perforator (TDAP) flap has been developed to improve the postoperative aesthetic and psychological states of patients who receive breast-conserving surgery (BCS); nonetheless, the TDAP flap exacerbates the pain that occurs at 2 surgical sites. Objectives: This trial aimed to compare the efficacy of the rhomboid intercostal block (RIB) and the serratus anterior plane block (SAB) as postoperative analgesics for BCS. Study Design: Prospective randomized controlled clinical trial. Setting: This clinical trial was conducted at Zagazig University Hospitals. Methods: Eighty-four patients scheduled for BCS followed by a TDAP flap were randomly divided into 3 groups (of 28 patients each). Group C received general anesthesia, and groups SAB and RIB received SAB and RIB blocks, respectively, followed by general anesthesia. The cumulative tramadol consumption within 24 hours after the operation was the primary outcome. The postoperative pain score, first-rescue analgesic time, and sensory block coverage were the secondary outcomes. Results: The 24-hour cumulative tramadol consumption and duration of the first rescue analgesic were significantly lower and longer, respectively, in the RIB group, than in the SAB group or the control group. The VAS score was lower in the RIB group than in the SAB or control group at all measurement times, except at 24 hours postoperatively, and the values among the groups were not significantly different. Dermatomal coverage of the anterior and posterior hemithorax extended from T2-T9 in the RIB group and from T2-T10 in the anterior hemithorax only in the SAB group. Limitations: Both block procedures were applied as single shots, and their impact on chronic postoperative pain was not assessed; the observation may therefore be drawn that a continuous local anesthetic (LA) infusion catheter could be used to extend the period of analgesia. Conclusion: Because of its ability to block both the anterior and posterior hemithorax, the RIB, is more efficient than the SAB at controlling acute pain and reducing opioid consumption in patients undergoing BCS followed by TDAP flaps; thus, the RIB can be employed as a potential alternative in these surgeries.