Lymph node metastasis is a major prognostic factor for patients with breast cancer. The activation of vascular endothelial growth factor (VEGF)-C plays a key role in lymph node metastasis through promoting lymphangiogenesis. Thus, we attempted to elucidate whether small interfering RNAs (siRNA) targeting VEGF-C could suppress lymphangiogenesis and lymph node metastasis in vivo. A lentivirus-based VEGF-C siRNA vector was infected into breast cancer cells and a xenograft model. The expression of VEGF-C mRNA and protein were quantified by quantitative real-time polymerase chain reaction (QRT-PCR), immunohistochemistry, and western blot analysis. The effect of VEGF-C siRNA on breast cancer cells was investigated by an invasion assay. Lymphangiogenesis was analyzed with anti-LYVE-1 and anti-D2-40 by immunohistochemical analysis. Lentivirus-mediated VEGF-C siRNA stably reduced VEGF-C mRNA and protein expression. VEGF-C siRNA inhibited the invasive ability of breast cancer cells in vitro. Five weeks after intratumoral injection, the tumor volume was significantly smaller in the VEGF-C siRNA group than in the control scramble siRNA group in the MDA-MB-231 cell xenograft model. The numbers of LYVE-1 and D2-40 positive vessels per microscopic field were significantly decreased in the VEGF-C siRNA group, which indicates that VEGF-C siRNA inhibited lymphangiogenesis. Moreover, lymph node metastasis was significantly suppressed by VEGF-C siRNA in vivo. In conclusion, these results indicate that lentivirus-mediated VEGF-C siRNA offers a new approach for therapeutic intervention to prevent tumor growth and lymphatic metastasis of breast cancer.