Purpose: To study the enhancing effect of ultrasound plus microbubble on siRNA transfection in vitro and in vivo.Methods: Human VEGF siRNA with 2’deoxy modification was used. The human CNE cells (from nasopharyngeal carcinoma) line was used for in vitro cell-based experiments and in vivo mouse xenograft model. Two different microbubble agents, BR14 and Levovist, were used together with the RNA transfection reagent RNA-mate. ELISA and RT-PCR assays were used to assess VEGF gene expression. Immunohistochemical staining (IHC) was performed to assess CD31 expression in xenograft tumors. Results: VdsR transfection in CNE cells abolished VEGF expression as determined by ELISA experiments. In the first mouse xenograft experiment, ultrasound exposure dramatically enhanced VdsR-mediated tumor inhibition. In the second mouse xenograft experiment, when VdsR was mixed with the microbubble reagents and then injected into xenografts, ultrasound exposure significantly reduced tumor growth in BR14-mixed VdsR group but not in the Levovist-mixed VdsR group compared to the control. RT-PCR experiments demonstrated that VEGF expression in ultrasound-exposed tumors was significantly lower than that in the control. Meanwhile, VEGF expression in the tumor tissue treated by BR14-mixed VdsR declined as compared with the controls. Tumor vascular density as measured by CD31 immunostaining was significantly decreased in ultrasound-exposed tumors compared to the control. Conclusion: Our data demonstrates that ultrasound exposure and/or micorbubble significantly help delivery of the siRNAs and enhances the efficiency of VdsR-mediated anti-tumor effects. These results indicate a possible clinical application of ultrasound plus microbubble as a location-specific enhancement approach for siRNA-based anti-cancer therapy.