The vascular endothelial growth factor receptor (VEGFR) is an important angiogenic target for cancer gene therapy. In this study, we designed an mRNA-cleaving oligodeoxynucleotide that targets the VEGF receptor 2 (VEGFR2) transcript (VEGFR2 DNAzyme). This DNAzyme was found to digest efficiently mRNA substrates of VEGFR2 in a concentration- and time-dependent manner. We also showed that the DNAzyme induces apoptosis and markedly inhibits endothelial cell growth compared with a disabled DNAzyme and untreated controls. In contrast, the DNAzyme did not inhibit the growth of MDA-MB-435 cells in vitro. The DNAzyme in complex with a nonviral carrier also significantly inhibited tumor growth in vivo. After the fourth injection, there was nearly a 75% reduction of tumor size in the DNAzyme-treated group compared with the saline-injected control group (P = 0.024). Marked cell death in the peripheral regions of the tumor accompanied by a reduction in blood vessel density is consistent with the antiangiogenic mechanism of the DNAzyme. This study indicates that DNAzymes, targeting angiogenic growth factors of tumors, show promise as antitumor agents.