Childhood obesity is a condition where excess body composition negatively affects a child's health or wellbeing. As methods to determine body composition directly are difficult, the diagnosis of obesity is often based on BMI. Due to the rising prevalence of obesity in children and its many adverse health effects it is being recognized as a serious public health concern. The term overweight rather than obese is often used in children as it is less stigmatizing. The Present study The Purpose of the study find out the effect of aerobic exercise with and without dieting regulations on flexibility and percent of body fat among obese school boys. The study was formulated as a true random group design, consisting of a pretest and posttest. The subjects (n=60) were randomly assigned to three equal groups of twenty obese school boys in each. The groups were assigned as Experimental Groups I, II and control group respectively. Pre tests were conducted for all the subjects on flexibility and percent of body fat. After the experiment period of twelve weeks post test scores were obtained. The difference between the initial and final scores was considered the effect of the experimental treatment. To test statistical significance, statistical tool ANCOVA was used to find out the effect of aerobic exercise and dieting regulations on obese school boys. It was found that aerobics exercise with and without diet were significantly better than control group in improving Flexibility of the obese school boys. Thus, it was found that Aerobics with diet was significantly better than Aerobics without diet and control group in reducing Percent Body Fat of the obese school boys.