The renal collecting duct (CD) contains two major cell types, intercalated (ICs) and principal cells (PCs). A previous report showed that deletion of β-1 integrin in the entire renal CD causes defective CD morphogenesis resulting in kidney dysfunction. However, subsequent deletion of β-1 integrin specifically in ICs, and PCs respectively did not cause any morphological defects in the CDs. The discrepancy between these studies prompts us to reinvestigate the role of β-1 integrin in CD cells, specifically in the PCs. We conditionally deleted β-1 integrin in mouse CD PCs using a specific AQP2 promoter Cre-LoxP system. The resulting mutant mice, β-1f/fAQP2-Cre+ had lower body weight, failed to thrive and died around 8 to 12 weeks. Their CD tubules were dilated and some of them contained cellular debris. Increased apoptosis and proliferation of PCs were observed in the dilated CDs. Trichrome staining and electron microscopy revealed the presence of peritubular and interstitial fibrosis that is associated with increased production of extracellular matrix proteins including collagen type IV and fibronectin, as detected by immunoblotting. Further analysis revealed a significantly increased expression of TGF-β induced protein, fibronectin, and TGF-β receptor-1 mRNAs, and concomitantly increased phosphorylation of SMAD-2 that indicates the activation of the TGF-β signaling pathway. Therefore, our data reveals that normal expression of β-1 integrin in PCs is a critical determinant of CD structural and functional integrity, and further supports the previously reported critical role of β-1 integrin in the development and/or maintenance of the CD structure and function.