Introduction <p>The rising global prevalence of obesity has established bariatric surgery as a key therapeutic option; however, postoperative pain management remains a challenge. This study investigated the influence of body mass index (BMI) stratification on acute postoperative pain in patients undergoing bariatric surgery.</p> Methods <p>Fifty-five patients aged 18–65&#xa0;years with BMI ≥ 30&#xa0;kg/m² scheduled for laparoscopic sleeve gastrectomy were categorized into the obesity group (O group; 30&#xa0;kg/m² ≤ BMI &lt; 40&#xa0;kg/m²) and the severe obesity group (SO group; BMI ≥ 40&#xa0;kg/m²). Preoperative pain threshold and pain tolerance threshold, perioperative inflammatory cytokines, Brief Pain Inventory (BPI) scores, Quality of Recovery-15 (QoR-15) scores, postoperative resting and movement numeric rating scale (NRS) scores, patient-controlled analgesia (PCA) pump usage, cumulative analgesic consumption, and analgesic satisfaction were assessed.</p> Results <p>Compared with the O group, the SO group demonstrated a significantly higher pain tolerance threshold (4.1 ± 0.8 vs. 3.5 ± 1.0, <i>P</i> &lt; 0.01), along with lower demand for PCA and reduced consumption of cumulative morphine milligram equivalents and flurbiprofen (<i>P</i> &lt; 0.05). Notably, the primary outcome, the 24-h BPI score, showed no significant difference between the two groups. On postoperative days 1 and 3, tumor necrosis factor-α (TNF-α) levels were significantly lower in the O group, whereas no significant intergroup differences were observed in other inflammatory cytokines. No significant differences were observed in NRS or QoR-15 scores between the two groups.</p> Conclusion <p>BMI may be considered as a factor for stratifying postoperative analgesia, favoring multimodal, opioid-sparing strategies in patients with severe obesity who demonstrate higher pain tolerance and lower analgesic requirements.</p> Trial Registration <p>Chinese Clinical Trial Registry, ChiCTR2400095080.</p>