Objective:To investigate the effect of in vivo shRNA plasmid vector gene transfer to silence OPN expression upon epithelial to mesenchymal transition of the tubular epithelial cells (TECs) in rat chronic allograft nephropathy (CAN) models, and to explore the possible role of OPN in CAN. Methods: Orthotopic renal-transplantation using F344 rats as donors and Lewis rats as recipients was operated to establish Allo group, while transplantation from Lewis to Lewis rats as Syn group. Hydromechanics based gene transfer method was used to establish RNAi and EV groups, for which OPN-shRNA or empty vector was injected into the renal vein. Rats in each group were sacrificed 12 weeks after the surgery. Allograft samples were collected and sectioned for HE staining, masson’s trichrome staining, immunohistochemical study and Western blot assay. Results: The morphological changes of allograft in Allo/EV group consist with CAN. Compared with the Syn group,Western blot showed a significant rise of OPN expression. In the RNAi group, the OPN expression was significantly reduced(P < 0.05) compared with Allo/EV group. The RNA interference inhibited EMT of TECs and the pathogenesis of CAN, which were confirmed by immunohistochemistry and HE/Masson’s trichrome lightscopy. Conclusion:The OPN expression in rat CAN model was significantly up-regulated. The in vivo RNA interference inhibited the OPN expression. Inhibition of OPN can protect the allograft from pathogenesis of EMT and IF/TA in CAN.