Abstract: Objective:To study the effects of exercise training at the maximal fat oxidation(FATmax)intensity on body composition,cardiovascular fitness,and exercise ability in 9-to-10-year-old boys with obesity.Methods:Thirty-six(36)boys with obesity,aged 9~10 years,were randomly divided into the FATmax or non-exercise control group.FATmax was identified in a graded exercise test,and the intensity was applied to design the individualised exercise program for each subject.FATmax group took part in 10 weeks of exercise training.Body composition,cardiovascular fitness,and exercise ability were measured before and after experiments.Results:At the FATmax intensity,the trained boys had an average heart rate at 140±6 bpm and running speed at 4.0±0.7km/h.FATmax group increased body height while decreased body mass,body mass index,and abdominal fat mass(P<0.05 for all variables).VO₂ max,lung capacity,heart function index,1 min sit-and-up,and body flexibility were improved significantly(P<0.05 for all variables).No significant improvement was found in the control group after the experimental period.Conclusion:10 weeks of FATmax exercise training is safe and effective to treat obese children.