Chronic transplant dysfunction (CTD) is the leading cause of long-term renal allograft loss and is characterized by specific histological lesions including transplant vasculopathy, interstitial fibrosis and focal glomerulosclerosis. Increasing evidence indicates that aldosterone is a direct mediator of renal damage via the mineralocorticoid receptor (MR). The MR antagonist spironolactone is renoprotective in native chronic kidney disease, but its effects in CTD are unknown. We studied the effects of spironolactone treatment on CTD development in the Dark Agouti-to-Wistar Furth renal allograft transplant model, by treatment with 20 mg/kg spironolactone or vehicle daily by oral gavage from 2 days before transplantation (donors and recipients) throughout the experiment (12 wk, recipients). Dark Agouti-to-Dark Agouti isografts served as negative controls. Spironolactone significantly ameliorated the development of transplant vasculopathy in allografts by reducing the number of affected intrarenal arteries. In addition, spironolactone treatment showed a trend towards reduced proteinuria and focal glomerulosclerosis, and significantly reduced glomerular macrophage influx. However, spironolactone treatment did not affect interstitial fibrosis, interstitial macrophage influx, creatinine clearance, and systolic blood pressure. We conclude that spironolactone selectively ameliorates transplant vasculopathy and glomerular lesions in renal CTD in rats. These results suggest that spironolactone may have renoprotective potential as an adjunct treatment in renal transplantation to ameliorate CTD.