Objective   To observe the effects of urine on TGF-β1 and Smad3 expression in cultured human urethral fibroblasts and explore the mechanism of urethral scar fibrosis.    Methods   The human urethral fibroblasts were cultured and stimulated by urine or 350 μmol/L uric acid. The mRNA and protein expression of TGF-β1 and Smad3 were measured by PT-PCR and immunofluorescent staining

respectively. Collagen Ⅰlevels in the supernatants in different groups were detected by ELISA.    Results   TGF-β1 and Smad3 were detected in human urethral fibroblasts by immunofluorescent staining. After being presented with urine or uric acid at physiological concentration

both TGF-β1 and Smad3 in human urethral fibroblasts were increased significantly at both the protein and mRNA levels（P0.05）. By ELISA

the upregulation of Collagen Ⅰ  in the supernatant was also discovered at 24 or 48 h after stimulation with urine or uric acid.    Conclusion   Uric acid stimulation could increase the expression of TGF-β1 and Smad3. Uric acid probably take part in promotion of urethral scar fibrosis.