Abstract Angiogenesis is an effective target in cancer control. The antiangiogenic efficacy and associated mechanisms of acacetin, a plant flavone, are poorly known. In the present study, acacetin inhibited growth and survival (up to 92%; P < 0.001), and capillary-like tube formation on Matrigel (up to 98%; P < 0.001) by human umbilical vein endothelial cells (HUVEC) in regular condition, as well as VEGF-induced and tumor cells conditioned medium–stimulated growth conditions. It caused retraction and disintegration of preformed capillary networks (up to 91%; P < 0.001). HUVEC migration and invasion were suppressed by 68% to 100% (P < 0.001). Acacetin inhibited Stat-1 (Tyr701) and Stat-3 (Tyr705) phosphorylation, and downregulated proangiogenic factors including VEGF, endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), matrix metalloproteinase-2 (MMP-2), and basic fibroblast growth factor (bFGF) in HUVEC. It also suppressed nuclear localization of pStat-3 (Tyr705). Acacetin strongly inhibited capillary sprouting and networking from rat aortic rings and fertilized chicken egg chorioallantoic membrane (CAM; ∼71%; P < 0.001). Furthermore, it suppressed angiogenesis in Matrigel plugs implanted in Swiss albino mice. Acacetin also inhibited tyrosine phosphorylation of Stat-1 and -3, and expression of VEGF in cancer cells. Overall, acacetin inhibits Stat signaling and suppresses angiogenesis in vitro, ex vivo, and in vivo, and therefore, it could be a potential agent to inhibit tumor angiogenesis and growth. Cancer Prev Res; 6(10); 1128–39. ©2013 AACR.