Background: The basic region-leucine zipper protein c-Jun has been linked to cell proliferation, transformation, and apoptosis. However, a direct role for c-Jun in angiogenesis has not been shown. Methods: We used human microvascular endothelial cells (HMEC-1) transfected with a DNAzyme targeting the c-Jun mRNA (Dz13), related oligonucleotides, or vehicle in in vitro models of microvascular endothelial cell proliferation, migration, chemoinvasion, and tubule formation, a rat model of corneal neovascularization, and a mouse model of solid tumor growth and vascular endothelial growth factor (VEGF)–induced angiogenesis. All statistical tests were two-sided. Results: Compared with mock-transfected cells, HMEC-1 cells transfected with Dz13 expressed less c-Jun protein and possessed lower DNA-binding activity. Dz13 blocked endothelial cell proliferation, migration, chemoinvasion, and tubule formation. Dz13 inhibited the endothelial cell expression and proteolytic activity of MMP-2, a c-Jun–dependent gene. Dz13 inhibited VEGF-induced neovascularization in the rat cornea compared with vehicle control (Dz13 versus vehicle: 4.0 neovessels versus 30.7 neovessels, difference = 26.7 neovessels; P = .004; area occupied by new blood vessels for Dz13 versus vehicle: 0.35 mm² versus 1.52 mm², difference = 1.17 mm²; P = .005) as well as solid melanoma growth in mice (Dz13 versus vehicle at 14 days: 108 mm³ versus 283 mm³, difference = 175 mm³; P = .006) with greatly reduced vascular density (Dz13 versus vehicle: 30% versus 100%, difference = 70%; P<.001). Conclusion: DNAzymes targeting c-Jun may have therapeutic potential as inhibitors of tumor angiogenesis and growth.