This study was aimed to determine the possible therapeutic effects of tadalafil, a specific PDE5 inhibitor, on renal fibrosis induced by unilateral ureteral obstruction (UUO). Our results suggested that tadalafil treatment ameliorated renal fibrosis by reducing TGF-β expression and might have important clinical relevance since tadalafil is currently used clinically to treat erectile dysfunction and pulmonary hypertension.