Objective:To investigate the protective effects and mechanism of Shenyan 1 Prescription on renal fibrosis of unilateral ureteral obstruction (UUO) rats through TGF- β 1/Smad homologous 3 (Smad3) pathway regulating ferroptosis.Methods:Totally 48 male SD rats were divided into four groups: sham-operation group, UUO model group, and Shenyan 1 Prescription low-(10 drug/kg) , and high-dosage (20 crude drug/kg) groups according to random number table method, with 12 rats in each group. The UUO model was induced by the method of unilateral ureteral obstruction except for those sham-operation group. After modeling, rats received corresponding drugs or normal saline by gavage for 4 weeks, once per day. After 4 weeks, the body mass and the left kidney weight were measured. The 24 h urine protein and the levels of serum albumin (ALB), alanine aminotransferase (ALT), serum creatinine (SCr) and blood urea nitrogen (BUN) were detected by biochemical analysis method; the ROS level in renal tissue was measured using a chemical fluorescence assay kit, and the SOD and MDA levels in left renal tissue of rats were measured using ELISA method; the morphology of renal tissue and the specific blue staining of hemosiderin were observed using HE and Prussian blue staining methods, respectively; the expressions of transforming growth factor-β1 (TGF-β1), Smad3, glutathione peroxidase 4 (GPX4), and solute carrier family 1 member 5 (SLC1A5) were detected by Western blot.Results:Compared with the model group, the 24 h urinary protein excretion in Shenyan 1 Prescription high-dosage group decreased ( P<0.05), the serum ALB level increased ( P<0.05), the ALT level decreased ( P<0.05), and the expression of SLC1A5 in renal tissue decreased ( P<0.05); the left kidney weight/body decreased in Shenyan 1 Prescription low- and high-dosage groups ( P<0.05); the levels of serum ROS and MDA decreased ( P<0.05), and the activity of SOD significantly increased ( P<0.05); the expressions of TGF-β1 and Smad3 in renal tissue decreased ( P<0.05), and the expression of GPX4 increased ( P<0.05), and the renal pathological injury and ion deposition were improved. Conclusion:Shenyan 1 Prescription has a protective effect on the structure and function of renal tissues in UUO rats through regulating ferroptosis via inhibition of the TGF-β1/ Smad3 pathway to inhibit renal fibrosis of UUO rats.