Though belatacept is administered with a weight-based dosing schema, there has been higher clearance reported in obese patients. Therefore, we evaluated the association between body mass index (BMI) and transplant outcomes in kidney transplant recipients who were randomized to cyclosporine- or belatacept-based immunosuppression in the BENEFIT and BENEFIT-EXT randomized clinical trials. A total of 666 and 543 patients underwent randomization and transplantation in BENEFIT and BENEFIT-EXT, respectively, of which 1056 had complete data and were included in this analysis. Patients were grouped categorically according to BMI: <25, 25 to <30, and ≥30 kg/m. BMI did influence both the incidence and severity of acute rejection. Obese patients with BMI >30 kg/m in the low intensity belatacept group experienced significantly more rejection at 12 months than did patients with BMI <25 kg/m or BMI 25 to <30 kg/m. In both the moderate intensity belatacept and low intensity belatacept groups, obese patients with BMI >30 kg/m experienced significantly more severe acute rejection than did patients with BMI < 25 kg/m or BMI 25 to <30 kg/m. These results suggest that obese kidney transplant recipients are at an increased risk for acute rejection when under belatacept-based immunosuppression when compared to nonobese patients.