Like anti-Fas monoclonal antibodies, some monoclonal antibodies against tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors have tumoricidal activity too. In this article we report a novel mouse anti-human DR5 monoclonal antibody, AD5-10, that induces apoptosis of various tumor cell lines in the absence of second cross-linking in vitro and showed strong tumoricidal activity in vivo. AD5-10 does not compete with TRAIL for binding to DR5 and synergizes with TRAIL to induce apoptosis of tumor cells. AD5-10 induces both caspase-dependent and caspase-independent cell death in Jurkat cells, whereas TRAIL induces only caspase-dependent cell death. We show for the first time that DR5 can mediate caspase-independent cell death, and DR5 can mediate distinct cell signals when interacting with different extracellular proteins. Studies on AD5-10 help us to understand more on the functions of DR5 and may provide new ideas for cancer immunotherapy.