Objective To investigate the concentration change of indoxyl sulfate (IS) in blood and the renal expression of renal fibrosis-related factors (transforming growth factor-beta 1, TGF-β1;fibronectin, FN) after administration of mutagenic lactobacilli by oral.Methods A total of 60 male Sprague-Dawley (SD) rats aged 6 weeks was divided randomly into 3 groups.The normal control group (Sham group, n =20) received Sham operation of just incision of skin without kidney removed.The other two groups of rats were renal failure models selected from survivals of the other 40 rats who received real operation with 5/6 of kidney removed.Finally, 35 survived renal-failure rats were divided randomly into 2 groups : pathological control group(Model group, n =17) who were administrated of 2ml sterile saline solution once a day by gavage, and experimental group (lactobacillus bulgaricus (LB) group, n =18) who were administrated of 2 ml mutagenic lactobacilli (1.5 × 108 cfu/ml) once a day by gavage.Eight weeks later, blood specimens were taken to test the concentration of IS with high performance liquid chromatography-fluorescence detection (HPLC-FLU), and urea and creatinine by automatic biochemical analyzer;moreover, the rats were killed to get kidney tissues for pathological examination.Results The levels of serum IS, urea, and creatinine were statistically significantly different between two groups (P ＜ 0.05).Both the levels of renal tubular damage and renal interstitial fibrosis were both lessen in the experimental group compared to the model group (P ＜0.05).TGF-β1 and FN expressions in renal tissues were significantly decreased (P ＜0.05).Conclusions Mutagenic lactobacilli not only reduces serum concentration of IS, urea and creatinine in renal failure rats but lowers the expressions of TGF-β1 and FN in renal tissues.