Background: Previous studies demonstrated that low Vitamin D levels are associated with hypertension, obesity, dyslipidemia, and diabetes mellitus, reflecting an increased cardiovascular (CV) risk burden. However, high levels can be associated with increased total and CV mortality. Hence, we aimed to evaluate the prevalence of Vitamin D deficiency and if it has a role in the occurrence of acute coronary syndrome (ACS). Patients and Methods: This study was carried out on 71 patients presented with ACS, undergoing coronary angiography at the cardiology department, Zagazig university hospitals. Exclusion Criteria: Disorders causing Vitamin D deficiency. Methods: All our patients were subjected to (1) careful history taking (2) thorough clinical examination (3) resting electrocardiogram (4) routine laboratory investigations beside thyroid, parathyroid hormone, Mg, Ph, and Vitamin D levels (5) echocardiography (6) coronary angiography. Results: In the present study, receiver operating characteristic curve analysis shows that the serum Vitamin D has a cutoff value ≤41.5 nm/L to predict ACS with 94.4% sensitivity and 83% specificity, a cutoff value ≤41.5 nm/L to predict unstable angina with 97.3% sensitivity and 83% specificity a cutoff value ≤52.625 nm/L to predict ST elevation myocardial infarction (STEMI) with 100% sensitivity and 76.6% specificity, and a cutoff value ≤41 nm/L to predict non STEMI with 100% sensitivity and 83% specificity. Conclusion and Recommendations: Vitamin D deficiency and insufficiency are common in patients with ACS. Further, larger multicenter studies are needed to assess Vitamin D level in ACS patients and to investigate its relationship with long term prognosis. Keywords: Acute coronary syndrome, Vitamin D deficiency, unstable angina, STEMI, NSTEMI