Childhood obesity is becoming more prevalent worldwide. The decrease in physical activity and increase in sedentary behavior are the major contributing factors to obesity. In this study 100 normal adolescents in the age group of 12-16 yrs were assessed for physical fitness through measurement of Vo2 max. Among the subjects, only 27% have achieved an average to good Vo2 max which showed the decreasing physical fitness of our adolescents. The boys and girls have achieved Vo2 max at a BMI of 17-19kg/m2 and 18-19kg/m2 respectively. This reiterates that BMI is an important determinant of Vo2 max. The Vo2max decreased above a waist circumference of 70cm indicating that increase in the amount of fat decreased the performance. The subjects have attained Vo2 max at a heart rate of 170-180 bpm, which showed that they have a good cardio respiratory fitness. The subjects who had achieved Vo2 max also had good physical activity levels as assessed by the questionnaire. This study paves way for encouraging physical activity among adolescents. Healthy lifestyles combining balanced diets of low energy density with increased levels of physical activity should be promoted among children.