Recent studies have suggested that sulforaphane, a compound found largely in cruciferous vegetables, could inhibit tumor growth through regulation of angiogenesis. However, the molecular mechanism by which it inhibits angiogenesis has not been reported. In this study, we examined the molecular mechanisms by which sulforaphane (SNF) inhibits angiogenesis through regulation of FOXO transcription factor in human umbilical vein endothelial cells (HUVECs). Inhibition of MEK/ERK and PI3K/AKT pathways synergistically inhibited cell migration and capillary tube formation by HUVECs and further enhanced the anti-angiogenic effects of sulforaphane. Inhibitors of MEK and AKT kinases synergistically enhanced nuclear translocation of FOXO3a. Inhibition of the MEK/ERK and PI3K/AKT pathways synergistically induced FOXO transcriptional activity and inhibited cell migration and capillary tube formation; these events were further enhanced in the presence of sulforaphane. Phosphorylation deficient mutants of FOXO enhanced antiangiogenic effects of sulforaphane by activating the FOXO transcription factor. In conclusion, activation of FOXO transcription factor by sulforaphane could be an important physiological process to inhibit angiogenesis which may ultimately control tumor growth. These novel antiangiogenic activities of sulforaphane are likely to contribute to its cancer chemopreventive and therapeutic potential.