AIM: We aimed to evaluate whether RDW has a predictive impact on weight loss after obesity surgery. MATERIAL AND METHODS: This was a single-institution retrospective study. Multiple linear regression analysis was used to determine the variables affecting the %EBMIL and %EWL values. Surgery of patients with %EMBIL > 50% and %EWL > 25% was considered successful. RESULTS: Hundred and ten patients were included in the study. The %EBMIL and %EWL values of patients with RDW>14.5% were lower. In the evaluation of successful surgeries, the probability of failure for those with RDW>14.5% is 10.93 times higher for %EBMIL and 21.55 times for %EWL. DISCUSSION: After the linear regression analysis, it was observed that the %EBMIL and %EWL were higher in the patients whose RDW values were 14.5 and below in the preoperative period. In these patients, it is an indication that more weight loss has occurred. Similar to our study, Wise et al showed that weight loss was greater with a decrease in the RDW value 10. CONCLUSION: Preoperative RDW value can be used as a predictor of weight loss and surgical success. It can provide an idea about whether the patient will lose enough weight and the success of the surgery.