To investigate the effect of the Uremic Clearance Granule (UCG, similar to), a Chinese patent medicine, on tubular epithelial-to-mesenchymal transition (EMT) in a unilateral ureteral obstruction (UUO) model in vivo and transforming growth factor (TGF)-beta 1 induced EMT of HK-2 cells in vitro. In vivo study, 50 Sprague Dawley rats were divided into three groups: a sham operation group (n=10), a UUO group (n=20), and a UUO with UCG treatment group (n=20). The UCG was given at a dose of 4.5 g/kg body weight per day by gavage after surgery. In vitro study, HK-2 cells were cultured in 10% fetal bovine serum (FBS), 10% healthy rat serum, 10% FBS and TGF-beta 1 (10 ng/mL), 10% healthy rat serum and TGF-beta 1, or 10% rat serum containing the uremic clearance granule and TGF-beta 1. The expression of the epithelial marker E-cadherin and the mesenchymal markers vimentin and alpha-smooth muscle actin (alpha-SMA) in kidney tissues and HK-2 cells were investigated by Western blot analysis and immunofluorescence staining. The rats of the UUO group showed obvious tubulointerstitial fibrosis, compared with the sham operation group rats. Tubulointerstitial fibrosis score was reduced by 17.5%+/- 1.1% at day 7 and by 20.0%+/- 1.2% at day 14 in the UCG-treated group, compared with the UUO group. The UCG could maintained expression of E-cadherin and suppressed expression of vimentin and alpha-SMA in kidney tissues of UUO rats at days 7 and 14, as determined by Western blot analysis and immunofluorescence staining. Rat serum containing the UCG partially inhibited TGF-beta 1-induced fibroblast phenotype of HK-2 cells and maintained the epithelial morphology of HK-2 cells in vitro. This occurred partially through a reduction of vimentin expression and an increase of E-cadherin expression. These results suggest that the UCG prevents tubular EMT and may be a promising agent for treating tubulointerstitial fibrosis.