Background: Although vascular gross calcification by radiologic study is known as an independent risk factor for cardiovascular morbidity and mortality in ESRD patients, the role of vascular micro-calcification (VMC) by pathologic evaluation is not well known. We have reported that VMC is associated with aortic stiffness as well as access patency in HD patients. This study was performed to evaluate other pathologic change saccompanied with VMC which may affect aortic stiffness and access patency in HD patients. Method: 30 ESRD patients receiving vascular access operation (radio-cephalic) who had been diagnosed to have VMC of radial artery by microscopic examination with von kossa staining and 29 ESRD patients without VMC were included. Expression of α-smooth muscle actin (α-SMA) and the main component of bone matrix, osteopontin were detected by immunohistochemistiry. Masson-Trichrome stain and Verhoeff van-Gieson stain was performed to identify fibrosis and elastic fiber. We compare the pathologic change and biochemical parameters between patients with VMC group and those without VMC group. Results: On pathologic examination, calcification was mainly located in the medial layer, those with VMC had higher prevalence of diabetes mellitus (84.8% vs 65.5%, p=0.043). VMC was associated with upregulation of osteopontin and diminished expression of α-SMA. Medial fibrosis was more frequently observed in the VMC (+) group than the VMC (-) group (35.1± 21.2% vs 11.3±6.2%, p=0.010). Degradation of elastic fiber was commonly observed in both group (VMC (+); 100%, VMC (-): 89.7%, p=0.143). Conclusion: This study showed that degradation of elastic fiber occurs before VMC and medial fibrosis is accompanied with VMC. Therefore, we suggest that medial fibrosis as well as VMC itself might play a role in aortic stiffness and access patency in HD patients. More studies are needed to establish the role of degradation of elastic fiber.