Background: COPD is a progressive disease characterized by persistent airflow limitation, due to chronic inflammation and structural changes and is the fourth leading cause of mortality. COPD patients suffer from progressive reduction of lung function, loss of exercise capacity, frequent disease exacerbations, and development of extrapulmonary comorbidities. Some studies indicate the possible association between COPD and vitamin D; however, the conclusion was not definite. Two meta-analyses on the roles of vitamin D in COPD have been conducted. Objectives of the Study: The objectives of the present study are to estimate the serum levels of 25OH vitamin D in COPD patients and to check association if any between vitamin D levels and severity of COPD. Methodol.: : Plain chest X-ray (PA view), Complete blood count was done by automated cell counter, liver, renal function tests and random blood sugar were determined using automated biochem. analyzer, Serum ionized calcium (Ca) was determined by ion selective electrode, ECG (ECG), Pulmonary function tests (PFTs) using 2130 spirometer and serum sample was used for Vitamin D levels measurement. Results: vitamin D levels were decreased in all categories of COPD patients as per the GOLD criteria. Discussion and Conclusion: The results of our study indicate that the serum vitamin D levels were lower in patients with COPD, severe COPD, and COPD exacerbation. Vitamin D deficiency is associated with increased risk of COPD and severe COPD but not COPD exacerbation. The results provided an improved understanding of the roles of vitamin D in COPD development and progression. Further prospective, large, and well-designed studies are needed to confirm the results.