The aim of this paper is to report the study on gene silencing efficiency of siRNA targeted against mouse VEGFR2 (siVEGFR2) in vitro mediated by polyethyleneimine (PEI) and its anti-tumor effect in vivo.  CY3-labeled siRNA was compounded into PEI and transfected into MS1 cells.  Confocal microscopy was used to image the subcellular distribution of siRNA in MS1 cells.  Semi-quantitative RT-PCR and Western blotting were used to evaluate VEGFR2 gene silencing induced by siVEGFR2/PEI complexes.  A tumor-bearing nude mice model was established to compare the anti-tumor effect after delivered by local and systemic routes.  siVEGFR2/PEI complex-transfected cells exhibited much fluorescence in cytoplasm with no evidence of nuclear accumulation.  The expression levels of VEGFR2 mRNA and protein in PEI-transfected cells were significantly down-regulated compared with that in blank group, the silencing efficiency were 28.2% and 23.6% respectively.  The tumor sizes in mice intratumorally injected with siVEGFR2/PEI complexes (189.429 ± 17.562 mm³) were reduced definitely compared to that in mice injected with siVEGFR2/PEI complexes via vein route (315.507 ± 20.491 mm³), or to saline groups (365.844 ± 20.713 mm³).  The study demonstrated that PEI could effectively transfect siRNA into cells and silence the VEGFR2 gene expression.  Intratumoral delivery is more suitable  for non-targeted modified PEI/siRNA complexes to inhibit the tumor growth in vivo.  The present data lay a solid foundation to further study on the gene silencing mechanism for PEI-medicated RNAi and its anti-tumor  efficiency in vivo.