Many studies believe that regular physical activity have health benefits by positively affecting cardiovascular endurance, muscular fitness, flexibility, and body composition improvement.The main interest of the present study was to evaluate the effect of aerobic exercise on selected physical fitness variables. The study design wasExperimental method. 20 male students of Chagni preparatory and secondary school aged 17-22 years had divided randomly into 2 equal groups, experimental (n=10) training group who performed in 3 days/week for 3-month aerobic exercise training program such as walking, jogging, running, rope skipping, step jump and ball games; whereas a control (n=10) group, did not perform this selected aerobic training unless both groups undergone normal physical education class program. Both groups had taken pre and post-testing and all the subjects participated in 4 physical fitness tests: cardiovascular endurance fitness was measured using 12 minute run test, muscular endurance was measured by push up test, flexibility was measured using sit and reach test and Body Composition was measured using BMI.The collected data were analyzed using paired t-test method Analysis with level of significant 5%. This result shows different results from pre to post test. The experimental pretest scores of the groups had significant difference from posttests scores (p=0.001). The result indicated that the mean value of experimental group cardiovascular endurance fitness before aerobic exercise was lower than that of aerobic exercise. This showed the improvement of cardiovascular endurance fitness after giving aerobic exercise was higher than before aerobic exercise. But the result indicated that the mean value of control group’s cardiovascular endurance fitness in the pre and posttest was relatively close each other. Hence, there were no significant difference between pre and post scores of control groups (p=.647). Generally, there was no significant difference in BMI between Experimental and Control groups during pre-training testing. There was a significant BMI reduction (P <0.05) in the experimental group after the training program.