Objective: Isolated coronary artery ectasia (iCAE) is characterized by localized or diffuse dilatation of the coronary arteries, and theexact mechanism underlying iCAE is unclear. However, endothelial dysfunction is related to iCAE. Adropin has a regulatory effectin the coronary artery endothelium. This study aimed to determine the relationship of adropin level to iCAE.Methods: Fifty patients with iCAE and 32 age- and sex-matched control subjects with normal coronary angiography (CAG) findings were selected from 4546 patients who underwent CAG between July 2019 and October 2019. Blood sample for adropinanalysis were collected just before CAG.Results: No significant difference was found between groups in terms of baseline characteristics and laboratory parameters. Themean adropin level in patients with iCAE was significantly lower than that in control subjects (0.33±0.35 vs. 0.55±0.35 ng/mL,p<0.001). In receiver operating characteristic analysis, the cut-off value of adropin ≤0.341 had 76.0% sensitivity and 84.37% specificity for predicting iCAE (area under the curve: 0.839, p<0.001). Multivariate analysis included age, left ventricular ejection fraction,and adropin level, which showed that adropin (per 1 ng/dL decrease) (odds ratio: 0.973 [0.956–0.990]; p=0.002) was independentlyassociated with iCAE.Conclusion: The present study showed that adropin level is significantly lower in patients with iCAE patients and is independentlyassociated with iCAE