Coronary artery ectasia (CAE) is the limitation or diffuse expansion of the epicardial coronary artery. In most cases, the pathological basis of CAE is considered to be coronary atherosclerosis. Previous studies have confirmed the association between Apelin and arterial atherosclerosis. Apelin-13 (AP-13) is the main serum Apelin subtype in healthy humans, however the effect of serum AP-13 on CAE has yet to be elucidated. In this research, we analysed the relationship between serum AP-13 levels and CAE.One hundred and forty subjects who underwent selective diagnostic coronary angiography were enrolled in this research. We identified and included 40 patients with CAE as the study subjects. Another 50 patients with coronary artery disease (CAD) were randomly selected as the CAD group, and 50 patients without CAD were selected as the normal control group. Serum AP-13 levels were collected for all subjects.There were no statistically significant differences in baseline data except for gender. After unconditional logistic regression analysis, AP-13 and HDL-c were independent risk factors for CAE (both p < 0.05). The serum AP-13 level was significantly lower in the CAE patients than in the CAD patients (1.86 ± 0.59 vs. 2.49 ± 1.19 ng/mL, p = 0.004). Serum AP-13 levels were slightly lower in the CAD patients than in the controls (2.49 ± 1.19 vs. 3.12 ± 1.64, p = 0.079).Apelin-13 may have an effect on the development of CAE. Further studies should be performed to elucidate the possible pathogenic role of AP-13 in CAE.