Background: Chronic Obstructive Pulmonary Disease (COPD) is one of the major causes of disability and fatality in the world along with posing a huge social and economic burden. World health organization estimated that COPD had been the cause of death in more than 3 million people around the globe. COPD is associated with significant and progressive irreversible airflow obstruction characterized by narrowing of the airways. Tobacco smoking has been observed to be the most common risk factor for COPD, with indoor air pollution, occupational dusts and chemicals adding on to the list of risk factors. On the other hand, Vitamin D been observed to play an important role in many of the biological processes including the respiratory process wherein, higher vitamin D concentrations have been associated with better lung function. Owing to the immune and anti-inflammatory functions on respiratory epithelium, role in lung tissue remodeling of vitamin D, and an observed deficiency of Vitamin D in patients with COPD, there could be a potential relationship between the two. Aims and Objectives- To evaluate the mean Vitamin D level according to COPD disease severity category as per GOLD criteria, to examine the relationship between serum Vitamin D levels and FEV1 at a sub-population level by categorizing the subjects based on gender, age, smoking status and BMI.