The extracellular domain of the tumor necrosis factor-related apoptosis-inducing ligand (sTRAIL) may function as a soluble cytokine to selectively kill various cancer cells without toxicity to most normal cells. We constructed a series of recombinant adeno-associated virus (AAV) vectors expressing the extracellular domain of human TRAIL fused with signal peptides of human insulin, interferon, human growth hormone, and serum albumin and designated them as AAV-ISN-T, AAV-IFN-T, AAV-HGH-T, and AAV-Alb-T, respectively. Transduction of human SMMC-7721 liver cancer cells with AAV-ISN-T led to higher levels of TRAIL(95-281) protein expression in the cell culture media and produced more apoptosis of the cells in vitro than those with AAV-IFN-T, AAV-HGH-T, and AAV-Alb-T. The therapeutic potential of AAV-ISN-T was then evaluated in a transplanted mouse model established by injection of human liver cancer SMMC-7721 cells subcutaneously. Subsequent oral or intraperitoneal administration of AAV-ISN-T resulted in a rapid, high level and long time expression of soluble TRAIL in the sera and livers of the animals, as well as effective suppression of tumor growth, with no toxicity to normal hepatocytes. These data strongly suggest that it is possible to increase soluble TRAIL expression to make full use of tumoricidal activity of TRAIL as a therapeutic strategy. In conclusion, we provide evidence that oral administration of AAV-TRAIL might be an important alternative route with practical significance for cancer gene therapy.