Objective:To investigate the expression of osteopontin in transplanted rat kidney and its relationship with chronic allograft nephropathy(CAN). Methods:Fisher(F344)kidneys were orthotopically transplanted into Lewis rat recipients(CAN group). Lewis to Lewis rat kidney transplantation was served as the control(control group). Renal function and urine protein excretion levels of the rats were analyzed. Animals were sacrificed 12 weeks post-transplantation for histological and immunohistochemical detection. Results:Renal function deteriorated progressively in the CAN group,and there was typical chronic allograft tubulointerstitial fibrosis observed in the kidneys. Immunohistochemistry staining showed that the positive rate of TGF-β1 expression in CAN group was 100%,higher than that in control group(0%). The positive rate of OPN expression in CAN group was 90%,while zero in control group. Compared with control group,the intensity of osteopontin increased along with the progression of CAN in CAN group. Conclusion:Our study suggests that the osteopontin plays an important role in the progression of CAN. The expression of osteopontin in epithelial cells could act as a molecular marker of CAN.