Introduction: Hypovitaminosis D may play unique role in the pathogenesis of Coronary Artery Disease (CAD), promoting accelerated atherosclerosis and subsequent cardiovascular events. Recent research has highlighted vitamin D deficiency as a novel cardiovascular risk marker, in addition to conventional and genetic risk factors. Objective: The objective of the study was to find out association between low vitamin D level and severity of coronary artery disease. Material and Methods: It was a cross sectional study carried out among 102 patients undergoing elective coronary angiography due to CAD in National Institute of Cardiovascular Diseases (NICVD), Bangladesh from May 2016 to April 2017. Serum 25-hydroxyvitamin D level of each patient was measured and categorized as deficient, insufficient and normal if the value were <20, 20 to <30 and ≥30 ng/mL respectively. Coronary Angiogram (CAG) was done during index hospitalization. The severity of the CAD was assessed by vessel score and Gensini score. Results: Out of 102 patients, 75 (73.5%) patients had vitamin D level <30 ng/ml, while 27 (26.5%) patients had normal level (≥30 ng/ml). Female patients had lower vitamin D level than male (Mean 20.4± 8.3 ng/ml vs 26.0± 10.1 ng/ml) (p=0.017). Double or triple-vessel CAD were more frequent in those with 25(OH)D levels <30 ng/mL as compared to those with normal levels (≥30 ng/ml) (p<0.001). Moderate to severe CAD (Gensini score ≥36) was found in 64.1% of patients with vitamin D insufficiency and 75.0% of patients with vitamin D deficiency (p<0.001). Serum vitamin D level inversely correlated with both vessel score (r=- 0.478, p<0.001) and Gensini score (r=-0.667, p<0.001). Multiple linear regression showed that vitamin D was associated with vessel score (β =-0.03, 95% CI=-0.05 to -0.02, p<0.001) and Gensini score (β =-1.2, 95% CI=-1.6 to -0.8, p<0.001) adjusting for diabetes mellitus, dyslipidemia and body mass index in the model. Conclusion: Serum vitamin D levels are inversely associated with angiographic severity of CAD. Low vitamin D level may be an emerging, independent and reversible cardiovascular risk factor.