Thiazolidinediones improve insulin resistance and endothelial dysfunction. However, the mechanisms underlying the vasoprotective effects of thiazolidinediones remain to be fully elucidated. The present study aimed to examine the molecular mechanism for the anti-vasoconstrictive effects of rosiglitazone in response to endothelin (ET) 1. Mouse aortas were treated with rosiglitazone for 24 hours, and ET-1-induced vasoconstriction was assessed by wire myography. The results showed that rosiglitazone attenuated ET-1-induced contraction in mouse aortas; this effect was abolished by ET-B receptor (ET(B)R) antagonist, NO synthase inhibitor, and by the removal of endothelium. By using Northern blotting, real-time RT-PCR, Western blotting, and immunohistochemical techniques, we found that rosiglitazone upregulated expression of ET(B)R at both mRNA and protein levels in mouse aortas and human vascular endothelial cells. The induction of ET(B)R was prevented by peroxisome proliferator-activated receptor-gamma antagonism. Luciferase reporter assay showed that rosiglitazone enhanced ETBR gene promoter activity. Furthermore, chromatin immunoprecipitation assays demonstrated that peroxisome proliferator-activated receptor-gamma can directly bind to ET(B)R gene promoter. Furthermore, in vivo treatment with rosiglitazone also attenuated the ET-1-induced vasoconstrictions and increased the ET(B)R expression in mouse aortas and mesenteric arteries. In conclusion, these results demonstrate that rosiglitazone attenuated ET-1-induced vasoconstriction through the upregulation of endothelial ET(B)R, which is a peroxisome proliferator-activated receptor-gamma direct target. (Hypertension. 2010; 56: 129-135.)