Background/Aims: Interleukin-6 (IL-6) is one of the inflammation biomarkers with highest predictive value for outcome in chronic kidney disease (CKD) patients. The present study aimed to determine the effects of indoxyl sulfate (IS) on IL-6 expression in vascular cells. Methods: IS was administered to normo- and hypertensive rats. Human umbilical vein endothelial cells (HUVECs) and human aortic smooth muscle cells (HASMCs) were incubated with or without IS. Results: Immunohistochemistry revealed that IS-administered rats showed increased expression of IL-6 in the aortic tissues. IS increased IL-6 expression in HUVECs and HASMCs in a time- and dose-dependent manner. Knockdown of organic anion transporter 3 (OAT3) using small interfering RNA (siRNA) inhibited IS-induced expression of IL-6 in HUVECs and HASMCs. IS induced activation of aryl hydrocarbon receptor (AhR) and nuclear factor-κB (NF-κB) subunit p65 in HUVECs and HASMCs. Both AhR siRNA and p65 siRNA inhibited IS-induced expression of IL-6. AhR siRNA inhibited IS-induced phosphorylation and nuclear translocation of p65 without change in total p65 level. However, p65 siRNA did not inhibit IS-induced nuclear translocation of AhR. Thus, AhR is responsible for IS-induced p65 signaling transduction. Conclusion: IS induces IL-6 expression in vascular endothelial and smooth muscle cells through OAT3/AhR/NF-κB pathway.