Recent studies from our laboratory showed that aldosterone plays a central role in the development of functional and structural injury induced by cyclosporine. These findings, however, do not allow us to establish if mineralocorticoid receptor antagonism could also be a helpful strategy to prevent chronic tacrolimus nephrotoxicity. This study was designed to evaluate if aldosterone participates in the renal injury induced by tacrolimus. For this purpose, four groups of male Wistar rats fed a low-sodium diet were studied: a vehicle group (V), spironolactone-treated rats (Sp 20 mg/kg), tacrolimus-treated rats (2 mg/kg) and rats treated simultaneously with tacrolimus+Sp for 28 days. At the end of the experimental period, mean arterial pressure , glomerular filtration rate (GFR) and renal blood flow (RBF) were measured. Tubulo-interstitial fibrosis (TIF), arteriolopathy percentage and arteriolar thickening were also quantified. Protein levels of TGF-β, phosho-Smad-3, Rho kinase (Rhok), Twist, and α-SMA were determined. In addition, endothelin and its receptor mRNA levels were quantified. Tacrolimus produced chronic nephrotoxicity characterized by significant decreases in GFR and RBF and significant increases in TIF, arteriolopathy, and arteriolar thickening. These alterations were associated with greater TGF-β protein and activity, as evidenced by a greater phosphorylation of Smad-3, which together with Rhok and Twist elevation promoted a greater epithelial-to-mesenchymal transition (EMT). In contrast, MR antagonism prevented TIF and reduced arteriolopathy, hypoperfusion and hypofiltration. The renoprotection conferred by Sp was associated with restoration of TGF-β and prevention of EMT.