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Abstract. Thiazolidinediones, peroxisome proliferators-activated receptor gamma (PPARγ) ligands, have been recognized as a potential therapeutic agents for the treatment of pathological neovascularization. In the present study, we examined the molecular mechanism by which troglitazone (TROG), a PPARγ agonist, exerts its inhibitory action in vascular endothelial growth factor (VEGF)-induced angiogenesis signaling. In an in vitro angiogenesis model using human umbilical vein endothelial cells, TROG (20 μM) significantly suppressed VEGF-induced cell proliferation and invasion of the cells into the Matrigel basement membrane, which was not reversed by treatment with PPAR antagonists, GW9662 (10 μM) and bisphenol A diglycidyl ether (10 μM). TROG also blocked VEGF-induced reactive oxygen species (ROS) production and its downstream extracellular signal-regulated kinase (ERK) phosphorylation, and this inhibitory effect was not reversed by GW9662 (10 μM). The antiangiogenic activity of TROG correlated with suppression of VEGF-induced matrix metalloproteinase (MMP)-2 and membrane type 1 (MT1)-MMP expression. In addition, the effects of TROG on VEGF-induced MMP-2 and MT1-MMP expression were comparable to those of the NADPH oxidase inhibitor diphenylene iodium (10 μM) and ERK inhibitor PD98056 (10 μM). Furthermore, in an in vivo angiogenesis system using a chick chorioallantoic membrane model, TROG dose-dependently inhibited VEGF-induced angiogenesis, which was similar to the inhibitory effect of N-acetylcysteine on VEGF-induced angiogenesis. The results suggest that the inhibitory effects of TROG on VEGFinduced angiogenesis were mediated through the suppression of VEGF-induced ROS production and ERK phosphorylation.