Background: Overweight and obesity prevalence has been increased worldwide creating a true pandemic and it is now affecting younger age groups. Objective: To determine the impact of Body Mass Index (BMI) on pulmonary function of late adolescents. Methods: A cross-sectional study was carried out among 95 late adolescents aged 18 to 22 Years. Participants were categorized into normal weight, overweight and obese groups based on their BMI. Pulmonary function was measured by a digital spirometer (Spirolab, GIMA/ Italy) following the American Thoracic Society guidelines. Results: The lowest FEV1/FVC ratio was found in obese females. The influence of BMI on Forced Vital Capacity (FVC), Forced Expiratory Volume in one second (FEV1), and Peak Expiratory Flow (PEF), in both males and females, was statistically insignificant. The BMI has an insignificant effect on the small airway parameters (FEF 50%, FEF 75%, and FEF 25%-75%) of the two sexes. A significant negative correlation was observed between BMI and FEV1/FVC in both males and females. Furthermore, a significant negative correlation was found between BMI and forced expiratory flow 50% (FEF50%) in males but not in females. Conclusion: A high BMI has an insignificant impact on most of the lung function parameters of adolescents, except for the FEV1/FVC ratio.