Vascular endothelial cell growth inhibitor (VEGI) is a member of the tumor necrosis factor superfamily and plays an important role in vascular homeostasis. In this study, to investigate the anticancer therapeutic potential of this gene, a secreted isoform of VEGI (VEGI-251) was inserted into a selectively replicating adenovirus with E1B 55 kDa gene deletion (ZD55) to construct ZD55-VEGI-251. We report here that secreted VEGI-251 produced from ZD55-VEGI-251-infected cancer cells potently inhibits endothelial cell proliferation, tube formation in vitro and angiogenesis of chick chorioallantoic membrane in vivo. Additionally, ZD55-VEGI-251 infection leads to a much more severe cytopathic effect than control viruses on several human cancer cell lines, including cervical cancer cell line HeLa, hepatoma cell line SMMC-7721 and colorectal cancer cell line SW620. Further study reveals that the increased cytotoxicity is a result of VEGI-251 autocrine-dependent, mitochondria-mediated apoptosis accompanied by caspase-9 activation, enhanced caspase-3 activation and PARP cleavage. Moreover, ZD55-VEGI-251-treatment of athymic nude mice bearing human cervical and colorectal tumor xenografts markedly suppressed tumor growth. Our findings indicate that the combined effect of antiangiogenesis and apoptosis-induction activity makes the VEGI-251-armed oncolytic adenovirus a promising therapeutic agent for cancer.