Aim: To evaluate aerobic capacity in trained and untrained subjects by measuring Vo2 max. Methods and Materials: In the present study 40 healthy subjects were selected between the age group 20-30 years. One group is not having any regular specific physical exercise and the second group which includes subjects, who regularly do the cycling in gym since more than two years. Resting pulse rate was recorded with E.C.G. The subjects were asked to peddle the bicycle ergo metre first with a resistance of 2 kg for 5 minutes next with a resistance of 4 kg for 3 minutes there after resistance is increased by 0.5 kg for every 3 minutes until the subject is exhausted. Immediately after the exercise heart rate was recorded with E.C.G. Vo2max =55.23-(0.09xheart rate/min). Results: P-value of Vo2 max is 0.005 which is highly significant. Conclusion: The Vo2 max is higher in trained subjects than in untrained subjects. This is due to cardiac output and total skeletal muscle mass are more in trained subjects.