Vascular changes in diabetes are characterized by reduced vasoconstriction and vascular remodeling. Previously, we demonstrated that TGF-β1 impairs Ang II-induced contraction through reduced calcium mobilization. However, the effect of TGF-β1 on Ang II-induced vascular remodeling is unknown. Therefore, we investigated the effect of TGF-β1 on Ang II-induced activation of the MAPK p44/42 pathway in cultured rat aortic smooth muscle cells (RASMC). Activation of MAPK p44/42 was determined with a phospho-specific antibody. Angiotensin type 1 receptor (AT<sub>1</sub>) and AT<sub>1</sub> mRNA levels were measured by [<sup>3</sup>H]candesartan-binding and real-time PCR, respectively. AT<sub>1</sub> gene transcription activity was assessed using AT<sub>1</sub> promoter-reporter constructs and by a nuclear runoff assay. In TGF-β1-pretreated cells, Ang II-induced phosphorylation of MAPK p44/42 was inhibited by 29 and 46% for p42 and p44, respectively, and AT<sub>1</sub> density was reduced by 31%. Furthermore, pretreatment with TGF-β1 resulted in a 64% reduction in AT<sub>1</sub> mRNA levels and decreased AT<sub>1</sub> mRNA transcription rate by 42%. Pretreatment with TGF-β1 blocked Ang II-induced proliferation of RASMC, while stimulating Ang II-induced upregulation of plasminogen activator inhibitor-1. In conclusion, TGF-β1 attenuates Ang II-mediated MAPK p44/42 kinase signaling in RASMC through downregulation of AT<sub>1</sub> levels, which is mainly caused by the inhibition of transcription of the AT<sub>1</sub> gene.