Objective To investigated the protective effect and immunology mechanism of Astragaloside Ⅳ(Ast) on rat renal ischemia-reperfusion injury model. Methods The SD rats were randomly divided into four group as the control, sham-operation, renal ischemia-reperfusion injury, and Ast treatment groups. Rat serum and urine were collected and detective for kidney function and interleukin cytokines. The kidney tissue was collected for histology exam. The rats in astragaloside group were intraperitoneally injected with 100 mg/kg astragaloside, and the other three groups were intraperitoneally injected with an equal volume of normal saline. The models of renal ischemia-reperfusion injury were prepared to generate in model and astragaloside groups, after 30 minutes of astragaloside injection. The rats with renal ischemia-reperfusion injury model were sacrificed after 24 hours, and the level of blood-urine creatinine, neutrophil gelatinase-associated lipocalin and Kidney damage molecule-1 were determined. The level of Th1 type cytokines (TNF-α, IFN-γ, IL-2) and Th2 type cytokines (IL-4, IL-5, IL-10) in serum were measured by using ELISA. The protein and gene expression of TNF-α, IFN-γ, IL-2, IL-4, IL-5, IL-10 in renal tissue were tested by western blot and PCR, respectively. The pathological changes and apoptosis of renal tissue in each group were detected by HE staining and TUNEL staining, respectively. The expression of CD20 protein in renal tissue was determined by immunohistochemistry. Results Compared with the model group, Ast treatment reduced serum creatinine (58.74 ± 9.44 μmol/L vs. 85.03 ± 23.48 μmol/L), increased creatinine clearance rate (0.81 ± 0.13 ml/min vs. 0.37 ± 0.08 ml/min), and reduce urine neutrophil gelatinase-associated lipocalin (NGAL) (579.34 ± 11.70 pg/ml vs. 827.60 ± 14.48 pg/ml), kidney injury molecule-1 (KIM-1) (105.06 ± 2.10 pg/ml vs. 151.67 ± 3.06 pg/ml) (P<0.05). Compared with the model group, Ast treatment alleviated renal tubular epithelial cell injury and significantly decreased the apoptosis (14.36 ± 1.36% vs. 28.63 ± 2.03%) (P < 0.05), and significantly decreased the serum TNF-α (361.44 ± 9.66 pg/ml vs. 515.93 ± 10.61 pg/ml), IFN-γ (64.11 ± 1.21 pg/ml vs. 93.51 ± 2.15 pg/ml), IL-2 (388.33 ± 1.21 pg/ml vs. 557.82 ± 15.29 pg/ml), IL-4 (60.89 ± 1.21 pg/ml vs. 95.56 ± 2.75 pg/ml), IL-5 (94.02 ± 2.81 pg/ml vs. 147.07 ± 3.50 pg/ml), and IL-10 (52.62 ± 2.51 pg/ml vs. 78.22 ± 3.24 pg/ml) (P<0.01). Compared with the model group, Ast treatment significantly decreased the kidney TNF-α mRNA (1.89 ± 0.59 vs. 2.87 ± 0.97), IFN-γ mRNA (3.11 ± 1.02 vs. 5.98 ± 1.52), IL-2 mRNA (1.68 ± 0.44 vs. 4.09 ± 1.65), IL-4 mRNA (2.41 ± 0.81 vs. 4.69 ± 1.62), IL-5 mRNA (1.56 ± 0.19 vs. 2.92 ± 0.55), IL-10 mRNA (1.45 ± 0.14 vs. 2.85 ± 0.32) (P<0.01). The ratio of IL-4 to IFN-γ was basically restored to the level of sham operation group (1.05 ± 0.02 vs. 1.02 ± 0.06) (P<0.01), and CD20 cells in renal tissue was reduced. Conclusions The Th1 and B lymphocytes play an important role in renal ischemia reperfusion injury, and Th2 cells play a protective role. Astragaloside can regulate the imbalance of Th1/Th2 in the early stage after acute renal injury, and alleviate renal tubular injury. Key words: Reperfusion injury; Astragaloside Ⅳ; Th1-Th2 balance; Antigens, CD20; Rats