Background and objective: Obesity is a serious __ampersandsignamp; widespread problem globally. Reduced cardio respiratory fitness in young adults has emerged as an important factor for developing cardiovascular co morbidities later in middle age. Maximum oxygen consumption (VO2max) is the internationally accepted parameter to evaluate cardio respiratory fitness. Numerous clinical investigations have established a strong association between low cardio respiratory fitness and mortality. Increased body fatness is an additional factor for developing cardiovascular diseases. Hence, the current study was designed to evaluate cardio respiratory fitness in terms of VO2max in young healthy males and to study the relation between body mass index and cardio respiratory fitness. Methodology: Hundred young healthy male subjects in the age group of 18 to 25 years were included in this study group. Body mass index was measured as weight in kilograms divided by height in meters square. Cardio-respiratory fitness in terms of VO2max was assessed by following the protocol of Queen__ampersandsignlsquo;s College Step Test. Results: There was a significant negative correlation between body mass index (BMI) and VO2max (ml/kg/min) (r = -0.66, p__ampersandsignlt;0.01). Conclusion: The results suggest the striking effect of body fatness on cardio respiratory functions. Excessive amount of body fat exerts an unfavorable burden on cardiac function and oxygen uptake by working muscles. Low cardio respiratory fitness in young adults with increased body fatness could be a factor for developing cardiovascular co morbidities later in middle age.