There is a dramatic rise in the prevalence of obesity among Egyptian children that has reached alarming levels.The purpose of this study is to compare between body mass index and percentage body fat using bioelectrical impedance.The present study is a cross sectional study that included 40 overweight and obese children and adolescents attending outpatient clinic of Diabetes Endocrine and Metabolism Pediatric Unit at Cairo University Children's Hospital. Also 20 healthy children age and sex matched were included as a control group.All screening groups (males and females) were subject to height, weight, BMI, subscabular and triceps skin fold thickness, neck circumference waist and hip circumference, waist/ hip ratio, BIA parameters.In our study, body fat content (kg), and body fat content (%) showed significant positive correlation to BMI, BMI percentile, and BMI Z score.BIA is an accurate technique for assessment of body composition, but it needs some precautions as the user should not exercise or perform any vigorous activity for at least 8 hours before the test to ensure accurate body fluid result.