Background: Adropin is a peptide hormone expressed in coronary artery endothelial cells, which plays a potential endothelial protective role. We sought to assess whether serum adropin levels are correlated with the coronary slow flow phenomenon (CSFP). Methods: We enrolled 82 patients with angiographically confirmed CSFP and 184 age-matched controls. Serum adropin levels were measured by enzyme-linked immunosorbent assay (ELISA), and coronary flow rate was assessed using thrombolysis in myocardial infarction (TIMI) frame count (TFC). CSFP was defined as a corrected TIMI-TFC greater than two standard deviations from the normal range. Results: Serum adropin levels were significantly lower in the CSFP patients (n = 82) than in the controls (n = 184) (4.03  1.99 vs. 4.86  1.88 ng/ml, p = 0.001). Multivariate logistic regression analysis revealed that serum adropin was the only independent negative predictor of CSFP (odds ratio 0.758, 95% confidence interval 0.647-0.888, p = 0.001). Serum adropin levels were independently and negatively correlated with mean TFC (r = -0.387, p < 0.001). Conclusions:We demonstrated that decreased serum adropin levelswere independently associated with the presence and severity of angiographically proven CSFP. These findings suggest that serum adropin may be a potential biomarker to provide valuable information regarding the prediction of CSFP.