Abstract: Objective To investigate the effects of leucine on body compositions, blood glucose and blood lipids in overweight/obese adult with type 2 diabetes mellitus, so as to provide the evidence for diabetic dietary therapy. Methods Thirty-four patients without insulin therapy were randomly divided into leucine intervention group and control group. The participants in the intervention group received 3 g of leucine per day. The study was lasted 3 months and the participants maintained their therapy and life style. The relative parameters were determined before and after the study. Results Thirty participants (15 in the intervention group and 15 in the control group) completed the study. There was no significant difference in body compositions, blood glucose and lipids between two groups at baseline. After intervention, the body weight decreased by 0.91 kg and 0.83 kg, and body protein increased by 0.17 kg and 0.30 kg in intervention group and control group, respectively. On the other hand, the fasting blood glucose decreased by 0.37 mmol/L in the intervention group and increased by 0.12 mmol/L in the control group. However, there were no significant differences in body weight, fat mass, muscle mass between the control and intervention groups. In addition, the plasma levels of fasting blood glucose, glycosylated hemoglobin and blood lipids were similar between two groups. Little change of these parameters was observed before and after the study. Conclusion Leucine supplementation of 3 g/day for 3 months has no effects on body compositions, blood glucose and blood lipids in overweight/obese adult with type 2 diabetes mellitus.