Aim: Bariatric surgery is an effective treatment for morbid obesity that has inevitable complications including postoperative bleeding and staple-line leakage. Erythrocyte sedimentation rate (ESR) can be a clinical indicator for prediction of leakage. Methods: This retrospective cohort study was done on 1999 patients who underwent sleeve gastrectomy in Erfan Niyayesh Hospital, Tehran, Iran. ESR levels of patients were evaluated in cases which had postoperative leak. Statistical analyses were performed using SPSS software. Results: Among the 2350 patients, 50 subjects experienced gastric leak (2.12%). ESR mean was 73.1 mm/h for cases, statistically significantly higher in patients with leakage compared to the control group. In addition, ESR serum level mean was 31.34 mm/h for control groups. Other variables including C-reactive protein and platelet count were not statistically significant. Conclusion: Higher ESR serum level can be seen in various conditions, and, in obese patients who undergo bariatric surgery, it can be a reliable predictor for postoperative gastric leak complication.