To investigate the effect of TIEG-siRNA on Smad2, p-smad2 and collagen IV in diabetic nephropathy rats induced by streptozotocin (STZ).Ten Sprague-Dawley rats injected with STZ were randomly divided into TIEG-siRNA and Control groups. Other five normal rats were used as control. Each of the TIEG-siRNA and Control groups were injected with TIEG-siRNA and Control 0.5 ml via tail vein at 0 and 72 hours respectively. All rats were sacrificed at week 4 after a successful modeling. To confirmed the efficacy of TIEG-siRNA in rat kidney, the TIEG levels were determined by fluorescence quantitative PCR. The expressions of Smad2, p-smad2 and collagen IV protein were detected by immunohistochemical method while Smad2 and p-smad2 examined by Western blot.The TIEG levels were greatly down-regulated in the TIEG-siRNA treated group (0.0636 ± 0.0066) versus the empty vector treated group (0.1054 ± 0.0111) (P < 0.05). The immunohistochemical semi-quantitative method indicated that there was a decrease in the TIEG-siRNA treated group versus the empty vector treated group: (2.13 ± 0.19)% vs (2.53 ± 0.34)% in Smad2, (21.77 ± 2.00)% vs (27.03 ± 2.51)% in p-smad2 and (3.67 ± 0.42)% vs (4.85 ± 0.43)% in collagen IV. Western blot also showed that smad2 in the TIEG-siRNA treated group (0.32 ± 0.09) was much lower than that in the empty vector treated group (0.50 ± 0.04). And p-smad2 in the TIEG-siRNA treated group (0.16 ± 0.01) was much lower than that in the empty vector treated group (0.32 ± 0.02) (P < 0.05).TIEG-siRNA may be useful in preventing the progression of diabetic nephropathy through influencing the expression of Smad2 and its activation and down-regulating collagen IV.