According to traditional Chinese medicine , Cordyceps sinensis (CS) can prevent subjects from renal failure. The aim of this study was to investigate the protective effect of CS preconditioning on ischemic renal acute failure in rats and to assess its mechanism. The animal model of ischemic acute renal failure was performed by left nephrectomy and clamping right renal vessel for 45 mins in S-D rats. Cordyceps group had been pretreated with two-day 600 mg/kg CS before I/R injury. Rats were sacrificed at 1, 3, 6, 16, 48 and 120 h after reperfusion for evaluation of renal function and histopathological PASD staining. The immunohistochemistry and Western blotting of SDF-1£\, CXCR4 and Ki67 were also performed. £E-galactosidase activity was detected with the senescence staining. The results showed that the level of creatinine in Cordyceps group were significant lower after 48 hours I/R injury (p =0.04). PSAD staining in Cordyceps group revealed less tubular necrosis, tubular dilatation, and cast formation at 6 and 16 hour than in control group. Immunohistochemistry of SDF-1£\ in Cordyceps group demonstrated staining in the distal tubules and collecting ducts at 1, 3, 6, and 16 h. The CXCR4 signal of control group had gradually intensified from 1 to 6 hr after I/R . In Cordyceps group, the CXCR4 expression had been stabilized until 16 h after I/R. The £]-galactosidase activity was higher in control group at 1, 3 and 6 hours. However, the senescence was presented at 1 and 3 hours in Cordyceps group. The nuclear staining of repair enzyme Ki67 in Cordyceps group showed higher density than in control group. Pathologic morphology indicated CS may protect subjects from ischemic acute renal failure. CS also induced SDF-1£\ expression in early stage of I/R injury, and maintained the stable CXCR4 expression. CS can not only reduce the activity of senescence-related £]-galactosidase, but also regulate the expression of repair enzyme Ki67, indicating that CS may alleviate the ischemic-induced senescence and enhance renal repair.