Objective: Although underlying mechanisms of coronary artery ectasia (CAE) are clearly unknown, destruction of extracellular matrix may be responsible for the ectasia formation. Thus, we investigated the role of matrix metalloproteinases (MMP-9) and inflammatory markers (hs-CRP)Methods: This study consisted of 30 consecutive CAE patients, 30 obstructive coronary artery disease (CAD) patients, and 20 controls with normal coronary arteries undergoing cardiac catheterization. Plasma levels of MMP-9 and hs-CRP were measured.Results: hs-CRP level was significantly higher in the CAE group than both in CAD and control groups (2.3 + 0.5, 1.19 + 0.54, 0.8 + 0.3 mg/l, respectively , both p =0.00), while , MMP-9 level was significantly higher in both CAE group and CAD than control groups (27.71 + 4.7, 25.2 + 4.1 , 18.6 + 3.3 ng/ml, respectively , both p =0.00). In subgroup analyses, MMP-9 level was significantly higher in CAE patients with multivessels involvement compared with those with single-vessel ectasia (29.4 + 3.1 vs. 25.2 + 5.5 ng/ml, P=0.01 ).while, hs CRP level was comparable in both groups ( 2.3 + 0.52 vs. 2.4 + 0.45 ng/ml, P=0.82).Conclusion: Our results suggest that the increased level of MMP-9, hs-CRP may be responsible for ectasia formation in patients with CAE and their plasma levels is correlated with the severty of CAE.