Myofibroblasts are defined as fibroblasts that express certain features of smooth muscle differentiation. Activation of myofibroblasts plays a central role in fibrosis. Transforming growth factor-β (TGF-β) is a potent activator of myofibroblasts; namely, TGF-β causes changes in myofibroblast phenotypes including morphological alterations and the expression of α-smooth muscle actin (α-SMA), a marker of myofibroblasts. Because it has been well known that humoral factors, especially, TGF-β, and extracellular matrix components cause myofibroblast activation, we examined the expression of integrin and related proteins during activation of MRC-5 human myofibroblasts with TGF-β. Western blot analysis revealed that TGF-β treatment for 3 days increased the expression of α-SMA, which was also immunocytochemically observed as actin stress fibers. In the early phase of TGF-β treatment, fibronectin expression was greatly increased, followed by the increased expression of integrin αv and α11 and integrin β1 and β3. Co-immunoprecipitation assays revealed that the integrin αv subunit was co-precipitated with integrin β1 and β3, and that integrin β1 was co-precipitated with α11, αv, α2, and α5. The expression of focal adhesion kinase and integrin-linked kinase proteins was also upregulated by treatment with TGF-β. In addition, the expression of type I collagen mRNA was increased by TGF-β, but not type III collagen mRNA, as judged by real-time PCR analysis. These results suggest the possibility that TGF-β induces fibronectin expression in MRC-5 cells, which subsequently induces the expression of integrin receptors, αvβ3, αvβ1, and α11β1. This report also shows that expression of integrin α11 is upregulated during the TGF-β−mediated activation of myofibroblasts.