BACKGROUND Pain after laparoscopic cholecystectomy (LC) is multifactorial and usually not effectively treated. Rectus sheath block (RSB) has been proven to reduce the pain from midline abdominal incision and laparoscopic surgery. We investigated the preemptive analgesic effect of RSB after LC. METHODS In this prospective, randomized, single-center trial, 200 patients undergoing LC were randomized into preoperative RSB (pre-RSB) or postoperative RSB (post-RSB) group. An ultrasound-guided RSB was performed before skin incision in the pre-RSB group or after skin closure in the post-RSB group. The primary outcome was total rescue analgesic consumption at 24 h post-surgery. The secondary outcomes were cumulated rescue analgesic consumption and postoperative pain measured by numerical rating scale (NRS) at 0, 1, 2, 6, 9, 18, and 24 h post-surgery. RESULTS Total rescue analgesic consumption at 24 h post-surgery was significantly lower in the pre-RSB group than in the post-RSB group (p = 0.020). The cumulated rescue analgesic consumption was significantly lower in the pre-RSB group than in the post-RSB group at 1 h (p = 0.023), 9 h (p = 0.020) and 18 h (p = 0.002) post-surgery. NRS was significantly lower in the pre-RSB group than in the post-RSB group at 0 h post-surgery (p = 0.023). CONCLUSIONS The pre-RSB reduced the analgesic requirements in patients undergoing LC compared with the post-RSB.