The potential role of dietary fats in cancer is attracting considerable interest within the community. Both epidemiologic and experimental findings suggest that omega-3 polyunsaturated fatty acids (omega-3 PUFA), which are almost absent from typical Western diets, exert protective effects against cancer progression, although the precise mechanism of this suppression remains unknown. One of the potential targets for omega-3 PUFA in cancer suppression is angiogenesis, a process of new blood vessel formation within rapidly growing tumors. Here, we demonstrate that omega-6 PUFA stimulate and omega-3 PUFA inhibit major pro-angiogenic processes in human endothelial cells, including the induction of angiopoietin-2 and matrix metalloprotease-9, endothelial invasion and tube formation that are usually activated by the major omega-6 PUFA arachidonic acid. The cyclooxygenase (COX)-mediated conversion of PUFA to prostanoid derivatives participated in modulation of the expression of Ang2. Thus, the omega-6 PUFA-derived prostaglandin E2 augmented, whereas the omega-3 PUFA-derived prostaglandin E3 suppressed the induction of Ang2 by growth factors. Our findings are consistent with the suggestion that PUFA undergo biotransformation by COX-2 to lipid mediators that modulate tumor angiogenesis which provides new insight into the beneficial effects of omega-3 PUFA.