Introduction: The aim of this study was to evaluate the effects of a physical activity program for 4 months on aerobic capacity and on rating of perceived exertion exercise test in obese children according to their gender. Method: fourteen children (8 boys vs. 6girls) who participated in an exercise program for 4 months at 4 sessions per week with an intensity of 70 to 85% of maximum heart rate observed in the initial exercise test. Results: For the boys group the Waist circumference loss was 2cm (P < 0.001), the percentage of Fat Body Mass (% FM) was decreased 2,6% (P < 0.001) and total Fat Free Mass (FFM) has increased 3,3kg (P < 0.001). For the girls group (GF), (WC) loss was 1cm (P < 0.05), the (% FM) was decreased 1.7% (P < 0.01) and total (FFM) has increased 2,7kg (P < 0.001). When we compared the variation of aerobic parameters between (GF) and (GG) , there were differences in maximal Metabolic Equivalent of Task (10,8% vs 4%, P = 0.2), in maximal workload (15% vs 3,3% P < 0.001) and in maximum Heart Rate (0,9% vs 3,5%; p=0.04). The scores of rating of perceived exertion at baseline and at the end were respectively for GG and GF (7,22