Abstract: In order to determine the clinical conditions and effect of obesity and sedentary life style among adolescents on the systemic oxidative stress, 58 obese young adolescents of both sexes, aged 11-14 years were collected for the study. Another group of 24 healthy normal non obese children of the same matched age and sexes were collected as control group. All cases and controls were exposed to full clinical history and examination, including weight, height and calculation of body mass index. Levels of free and esterified F2-isoprostanes in plasma, concentrations of vitamin C and vitamin E, were measured and levels of erythrocyte superoxide dismutase activity (SOD) as well as erythrocyte catalase activity were estimated. Total cholesterol and triglycerides levels were determined enzymatically as well as HDL and LDL cholesterol levels. Sedentary lifestyle, frequent soft drinks ingestion as well as fast food ingestion represented a common habit, with smoking among this age group as compared with control group. with significant increase in weight and BMI as compared with controls. A significant high levels of free and esterified F2- isoprostanes, total cholesterol levels, HDL cholesterol and LDL cholesterol were detected among obese adolescents as compared with control group. While significant low levels of vitamin C, vitamin E, SOD and catalase enzymes were detected among obese adolescents as compared with control group. We concluded that obesity with sedentary lifestyle are highly associated with systemic oxidative stress, which is reflected on their health and school performance.