Introduction: Pulmonary function tests (PFTs) are critical tools in evaluating respiratory health by measuring lung capacity, airflow, and overall pulmonary performance. These tests provide insights into various respiratory disorders and help assess the impact of different physiological and environmental factors on lung function. Among the numerous factors influencing pulmonary function, body mass index (BMI) has emerged as a significant determinant. Methods: A Cross-sectional study was done at Department of Physiology NMMC Ahmedabad. The selection of samples based on their body weight. The present study included 120 participants (60 males and 60 females). All participants aged 18-20 years who are apparently healthy. Male and female according to BMI categorized into two groups, i.e., BMI < 25 and BMI > 25. Results: Respiratory parameters such as FVC, FEV1, FEV1/FVC, and PEFR are found to be significantly lower in female participants in comparison to male participants as shown in Table 1. The correlation of different pulmonary function parameters with BMI of the male and female participants are presented in Tables 2 and 3. It is observed that respiratory parameters such as FVC, FEV1, FEV1/FVC, and PEFR of both male and female participants correlated positively with BMI < 25 but there were substantial lung function losses with increasing BMI > 25, i.e., PFTs were negatively correlated. Conclusion: Obesity influences the respiratory function enhancing dyspnoea and increasing both cardiac load and respiratory muscle fatigue of the thoracic wall and the diaphragm due to the higher pressure exerted by intraabdominal adipose accumulation. In our study the results showed that increase in BMI had an inverse relationship with FVC, FEV1 and PEFR in obese when compared to the normal weight subjects.