Objective: To explore the influence of AD-VEGF-siRNA on the expression of vascular endothelial growth factor (VEGF) in neoplasm and blood serum.Methods: Transplantable model of human osteosarcoma was successfully established by the way of subcutaneous injection of VEGF highly expressed human MG63 osteosarcoma cells.These mice were divided randomly into three groups: AD-VEGF-siRNA group, 15 mice; AD-EGFP group, 15 mice; PBS group, 15 mice.Three mice were additionally raised without any treatment.The drug was injected intratumorally 200 IJL at each time, once a day.The total dose of virus was 2×109 pfu.Three osteosarcoma-bearing mice of each group were sacrificed at 11th, 14th ,17th day after the implantation of MG63 cells.The expression of VEGF in implanted tumors and blood serum was detected by ELISA methods.Then the left mice were all sacrificed at the end of experiment (19th day).The expression of VEGF in implanted tumors was detected by RT-PCR and immune histochemistry methods, and that in implanted tumors and blood serum was detected by ELISA methods.Results: (1) Tumors in mice could be seen at 5th day from the implantation of MG63 ceils.(2)The expression of VEGF could be detected in all groups by RT-PCR and immune histochemistry, Which was much lower in the group receiving AD-VEGF-siRNA therapy than two control groups (P＜0.05).(3) The expression of VEGF in blood serum of osteosarcoma-bearing mice was much higher than that of three healthy mice by ELISA (P＜0.05).(4) The expression of VEGF in blood serum and neoplasm in AD-VEGF-siRNA group was much lower than that in two control groups (P＜0.05).Conclusion: AD-VEGF-siRNA could effectively inhibited VEGF expression in vivo.This technology would bring some good references for our therapy of antiangiogenesis in osteosarcoma.