The increasing prevalence of sedentary lifestyles among adolescents has become a significant public health concern, contributing to obesity, cardiovascular diseases, and poor physical fitness. This study aims to evaluate the impact of an 8-week aerobic training program on the physical fitness of sedentary school boys aged 12 to 15. A total of 50 participants were randomly divided into two groups: an experimental group (n=25) that participated in a structured aerobic training regimen and a control group (n=25) that maintained their regular sedentary routines. The aerobic training included running, cycling, and jump rope exercises conducted four days a week for 45 minutes per session. Pre- and post-intervention assessments measured cardiovascular endurance (VO2 max), body mass index (BMI), and resting heart rate.