Melanoma differentiation-associated gene-7/interleukin-24 (mda-7/IL-24), identified by subtraction hybridization in the mid-1990s, is a potent gene therapeutic for cancer. Using a replication-deficient adenovirus as vector, it provokes apoptosis in diverse cancer cells without harming normal cells or tissues. To exploit the anticancer capability of IL-24 to the best, in this study, we generated a novel gene-virotherapy agent MUD55-IL-24, utilizing a replication-competent oncolytic adenovirus MUD55 as the gene delivery vector. It was documented that MUD55-IL-24 exhibited much stronger antitumor activity on gastric carcinoma both in vitro and in vivo, and its safety was comparable to the replication-deficient adenovirus Ad-IL-24. The unique properties of IL-24, including apoptosis induction, antiangiogenesis, and antimigration, were all significantly enhanced in MUD55-IL-24. After looking into the underlying mechanism, we found that intracellular ROS (Reactive Oxygen Species) generation may have caused the induction of apoptosis, mitochondrial dysfunction, and the activation of caspases in MUD55-IL-24-infected SG-7901 cells. Taken together, these results suggest that MUD55-IL-24 may be able to provide a potential strategy for future treatment of human gastric carcinoma.