Angiogenesis is known as a crucial process in the growth and spreading of tumor cells. Accordingly, the effective inhibition of this process would appear to be a promising way to cure angiogenesis-related diseases, including cancer. This study demonstrates that acalycixenolide E (AX-E) from the marine organism Acalycigorgia inermis exhibits a potent anti-angiogenic activity both in vitro and in vivo. AX-E inhibits the bFGF-induced proliferation of HUVECs in a dose dependent manner, along with the bFGF-induced migration, invasion, and tube formation of HUVECs. Moreover, AX-E potently inhibits the in vivo neovascularization of the chorioallantoic membranes (CAMs) of growing chick embryos. interestingly, AX-E suppresses the expression of metalloproteases 2 and 9, yet shows no effect on their activities. The novel chemical structure and potent anti-angiogenic activity of AX-E will be of great value in elucidating the molecular mechanism of angiogenesis as well as in the development of a novel anti-angiogenic drug.