Objective— Transforming growth factor-β–activated kinase 1 (TAK1) is a mitogen-activated protein 3-kinase and an AMP-activated protein kinase (AMPK) kinase in some cell types. Although TAK1 −/− mice display defects in developmental vasculogenesis, the role of TAK1 in endothelial cells has not been investigated in detail. Approach and Results— TAK1 downregulation (small interfering RNA) in human endothelial cells attenuated proliferation without inducing apoptosis and diminished endothelial cell migration, as well as tube formation. Cytokine- and vascular endothelial growth factor (VEGF)–induced endothelial cell sprouting in a modified spheroid assay were abrogated by TAK1 downregulation. Moreover, VEGF–induced endothelial sprouting was impaired in aortic rings from mice lacking TAK1 in endothelial cells (TAK ΔEC ). TAK1 inhibition and downregulation also inhibited VEGF–stimulated phosphorylation of several kinases, including AMPK. Proteomic analyses revealed that superoxide dismutase 2 (SOD2) expression was reduced in TAK1-deficient endothelial cells, resulting in attenuated hydrogen peroxide production but increased mitochondrial superoxide production. Endothelial cell SOD2 expression was also attenuated by AMPK inhibition and in endothelial cells from AMPKα1 −/− mice but was unaffected by inhibitors of c-Jun N-terminal kinase, p38, extracellular signal–regulated kinase 1/2, or phosphatidylinositol 3-kinase/Akt. Moreover, the impaired endothelial sprouting from TAK ΔEC aortic rings was abrogated in the presence of polyethylene glycol-SOD, and tube formation was normalized by the overexpression of SOD2. A similar rescue of angiogenesis was observed in polyethylene glycol-SOD–treated aortic rings from mice with endothelial cell–specific deletion of the AMPKα1. Conclusions— These results establish TAK1 as an AMPKα1 kinase that regulates vascular endothelial growth factor–induced and cytokine-induced angiogenesis by modulating SOD2 expression and the superoxide anion:hydrogen peroxide balance.