A further understanding of tumor angiogenesis is urgently needed due to the limited therapeutic efficacy of anti-angiogenesis agents. However, the origin of endothelial cells (EC) in tumors remains widely elusive and controversial. Snail has been thoroughly elucidated as a master regulator of the epithelial-mesenchymal transition (EMT), but its role in endothelium generation is not yet established. In this study, we reported a new and unexpected function of Snail in endothelium generation by breast cancer cells. We showed that high Snail-expressing breast cancer cells isolated from patients showed more endothelium generated from these cells. Expression of Snail was positively correlated with endothelial markers in breast cancer patients. The ectopic expression of Snail induced endothelial marker expression, tube formation and DiI-AcLDL uptake of breast cancer cells in vitro, and enhanced tumor growth and microvessel density in vivo. Snail-mediated endothelium generation depended on VEGF and Sox2. Mechanistically, Snail promoted the expression of VEGF and Sox2 through recruiting the p300 activator complex to these promoters. We showed the dual function of Snail in tumor initiation and angiogenesis in vivo and in vitro through activation of Sox2 and VEGF, suggesting Snail may be an ideal target for cancer therapy.