Inhibition of tumor angiogenesis through modulation of vascular endothelial growth factor (VEGF) and its signaling pathway has been clinically validated as a viable therapeutic modality in the treatment of cancer. The use of artificial transcription factors based on Cys2-His2 zinc-finger proteins (ZFPs) targeting the VEGF promoter offers a novel strategy for modulating VEGF levels in tumors. In order to demonstrate the utility of VEGF-targeted ZFPs as therapeutic agents, we generated adenoviruses (Ads) expressing VEGF promoter-targeted transcriptional repressor ZFP, F435-KOX. A replication-incompetent Ad expressing F435-KO X, namely, Ad-DeltaE1-KOX, significantly reduced VEGF expression and functionally led to inhibition of angiogenesis. In vivo, an oncolytic Ad expressing F435-KOX, namely, Ad-DeltaB7-KOX, elicited a pronounced antitumor effect against a human glioblastoma xenograft model, U87MG. Further, consistent with its expected mechanism of action, Ad-DeltaB7-KOX was shown to greatly reduce the level of VEGF and vessel density in tumor tissue and increase terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive apoptotic cells in tumors. Survival rates were also significantly increased in Ad-DeltaB7-KOX-treated mice. Taken together, the findings from this study identify F435-KOX as a novel and potent ZFP transcription factor that can inhibit VEGF-A-mediated angiogenesis and offer a novel therapeutic modality in the treatment of cancer.