Background: Although coronary artery ectasia (CAE) is thought to be a different form of vascular remodeling due to atherosclerosis, often links to endothelial inflammation and disturbance but the underlying mechanism that clearly explain this vascular abnormality is still yet unknown. Our study aimed to assess the correlation between Matrix Metaloproteinase-9 (MMP-9) levels and Reticulocyte Distribution Width (RDW) in coronary artery ectasia formation in CAD patients. Methods: Both basic demographic, laboratory, and angiographic data of forty-eight patients were collected and analyzed. We divided them into two groups according to coronary angiography results, where coronary artery ectasia was in the first group and obstructive coronary artery disease was in the second group. MMP-9 and RDW levels were compared between the two groups to find if there is a relationship with coronary artery ectasia. Results: The mean MMP-9 and RDW of the coronary artery ectasia group was higher than that of CAD group. (ROC) Curve analysis for detection of CAE cutoff regards RDW and MMP-9 in the two groups showed significant results with area under curve was 0.94, 0.97 respectively. Conclusion: The coronary artery ectasia was associated with the higher levels of MMP-9 and RDW. The reticulocyte distribution width (RDW) assay seems to be a simple method to predict Coronary Artery Ectasia. Recommendations: We see that RDW is a part of complete routine blood count which seems to be a simple, easy, inexpensive, routinely reported laboratory test may be a useful biomarker to predict coronary artery ectasia in suspected CAD patients. We need future investigation to find the effect of (RDW & MMP-9) biomarker in the prognosis and the risk stratification of patients with CAE. Key words: matrix metalloproteinase-9, reticulocyte distribution width, the isolated coronary artery ectasia.