Background: Indoxyl sulfate is a uremic toxin that accelerates the progression of chronic kidney disease (CKD). Serum levels of indoxyl sulfate are increased in dialysis patients. It was reported that indoxyl sulfate plays a role in endothelial dysfunction in uremic patients, and stimulates proliferation of rat vascular smooth muscle cells (VSMC). We examined associations between indoxyl sulfate and several markers related to atherosclerosis. Methods: The association between indoxyl sulfate and atherosclerotic risk factors was studied in 224 hemodialysis (HD) patients (123 male, 101 female). Serum levels of indoxyl sulfate were measured by using high-performance liquid chromatography (HPLC). Results: There were significant differences in serum levels of creatinine, calcium × phosphate and pentosidine between high- and lowindoxyl sulfate level groups. Indoxyl sulfate showed significant positive correlations with pentosidine, creatinine, and protein catabolic rate, and a significant negative correlation with high-density lipoprotein (HDL) cholesterol. Further, pentosidine, creatinine, and HDL-cholesterol were independently associated with indoxyl sulfate by multiple linear regression analysis. Conclusion: In addition to creatinine, pentosidine and HDL-cholesterol, the risk factors of atherosclerosis, were associated with indoxyl sulfate in HD patients. Indoxyl sulfate may be involved in the pathogenesis of atherosclerosis.