Abstract : <p>Obesity has been linked with increased morbidity and mortality although the causes of obesity are not well understood. Its&rsquo; obvious involvement in the respiratory system causing obesity hypoventilation syndrome (OHS), obstructive sleep apnoea(OSA) and abnormal pulmonary function is well known, but how the presence of excess fat in the body is involved in the various inflammatory or other disease of the respiratory system are not clearly known. In this presentation, we further explore the mechanism involved in alterations in lung function caused by obesity. It is observed that obese individuals have increased respiratory rates, reduced tidal volumes and decreased total lung compliance. The lung volumes are usually reduced, especially expiratory reserve volume. However, in most cases, airway resistance and gas exchange seem to be relatively well preserved. Obese individuals usually have mild hypoxemia due to ventilation- perfusion imbalance in bases of lung fields possibly due to micro atelectasis. Weight loss in such individuals to a large extent may reverse these changes.</p>