Objective To investigate the effect of body mass index on early postoperative clinical outcomes following off-pump coronary artery bypass grafting. Methods A total of 1062 patients that received OPCABG in Beijing Anzhen Hospital were recorded continuously from January 2015 to May 2015. The patients were divided into normal weight group(n=360), overweight group(n=527) and obesity group(n=175) according to their body mass index. The following outcomes in the ear-ly postoperative period were compared among the three groups: hospital mortality, atrial fibrillation and intra aortic balloon counter pulsation usage, multiple organ failure score system, postoperative score for cardiac surgery, sequential organ failure assessment score, respiratory index, and pressure-adjusted heart rate. Results The lowest mortality rate was observed in the overweight group(0.6％) in comparison with the normal weight group(2.2％) and obesity group(1.1％)(P<0.01). The lowest rate of atrial fibrillation was observed in the obesity group(20. 1％) in comparison with the normal weight group (22.1％) and overweight group(20. 7％)(P <0. 01). The IABP usage rate was the highest in the normal weight group (8. 1％), followed by the overweight group(6. 0％) and the obesity group(2. 9％)(P<0. 01). On the operation day and the first day after operation, the MODS, SOFA and PSCS scores of the obese group were significantly higher than those of the nor-mal weight group(P <0. 01). PaO2/FiO2 in the obese group was significantly lower than that in the normal weight group (P<0. 01). PAHR in the obese group was significantly higher than that in the normal weight group(P<0. 01). Conclusion High BMI groups were associated with lower rates of mortality, atrial fibrillation, and IABP utilization. The lowest mortality rate was observed in the overweight group.