Background: A few studies compared the vitamin D deficiency condition between the patients with the acute coronary syndrome (ACS) and those with stable coronary artery disease. The present comparative study aimed to assess the vitamin D deficiency status between the patients with ACS and those with stable coronary artery disease. Methods: This cross-sectional study was performed on 200 consecutive patients with the diagnosis of ACS or stable coronary artery disease. Serum Vitamin D level was measured by immunoassay and its serum level was categorized as normal (> 30 ng/ml), insufficient (20 to 30 ng/ml), and deficient (< 20 ng/ml). Results: Overall, 103 patients were categorized as stable angina group, 74 had unstable angina, 10 had STEMI, and 13 had NSTEMI. There was no difference in serum vitamin D3 level across the four groups including stable angina group (13.81 ± 15.13 ng/ml), unstable angina group (15.13 ± 11.11 ng/ml), STEMI group (21.58 ± 19.87 ng/ml), and NSTEMI group (18.67 ± 13.07 ng/ml) (p = 0.276). No difference was also found in the mean vitamin D3 level between the groups with new MI (15.98 ± 12.44 ng/ml versus 14.01 ± 15.31 ng/ml, p = 0.318). In total, 8.5% had normal vitamin D levels and 9.0% had vitamin D insufficiency, while the majority of patients (82.5%) were vitamin D deficient. The vitamin D deficiency was comparable in the patients with stable angina compared to those in ACS groups. According to ROC curve analysis, measuring serum vitamin D3 had a moderate value to discriminate stable angina from ACS (AUC = 0.651). In this regard, the best cutoff point for serum vitamin D3 level to discriminate stable angina from ACS was 9.0 ng/ml yielding a sensitivity of 70.1% and a specificity of 57.3%. Conclusion: The measurement of vitamin D and thus the presence of vitamin D deficiency have no sufficient power to discriminate ACS from stable coronary artery disease