Apoptin, a chicken anemia virus-derived protein, has been shown to induce apoptosis in various human cancer cell lines, but not in normal cells, thus making it a candidate for the development of novel therapeutic strategies. To enable the efficient transduction of tumor cells with apoptin, we have developed a novel mammalian expression system for the secretion of apoptin in vitro. We have previously shown the efficient and tumor-specific killing of cells by adding a secretory signal peptide (SP) to the N terminus of transacting activator of transcription (TAT)-apoptin (SP-TAT-apoptin). In addition, our report showed the successful secretion of high levels of TAT-apoptin/GFP into the culture medium from HUVEC cells infected by lentivirus LV-SP-TAT-apoptin/GFP. To obtain sustained apoptin-induced tumor cell death in vivo, we injected the LV-SP-TAT-apoptin viruses via the tail vein for systemic delivery of the viruses; viruses expressing LV-SP-TAT-GFP were used as a negative control. Markedly, almost all the hepatocellular carcinoma xenograft tumors disappeared following the treatment while the xenografts that received the control LV-SP-TAT-GFP viruses continued to grow. Moreover, the animal studies presented in this paper demonstrate a low toxicity of SP-TAT-apoptin in vivo, confirming and extending the results of the in vitro studies. Taken together, our data strongly suggest that systemic delivery of lentivirus-mediated secretable TAT-apoptin is feasible to eradicate liver cancer in vivo.