Livin, a novel member of the human inhibitors of apoptosis protein (IAP) family, plays an important role in tumor progression and occurrence by inhibiting cell apoptosis. It is selectively expressed in the most common human neoplasms and appears to be involved in tumor cell resistance to chemotherapeutic agents. To investigate its possibility as a therapeutic target for human malignancies, we established two genetically different stable tumor cell lines (LoVo and SPCA-1) and RNA interference (RNAi) technique was employed to downregulate Livin expression in two human tumor cell lines. The specific downregulation of Livin expression in tumor cell lines significantly inhibited in vitro cell proliferation and in vivo tumorigenicity. Furthermore, Livin knockdown led to cell arrest in the G1/G0 phase of cell cycle, eventual apoptosis and chemosensitivity enhancement in tumor cells. All these results indicate that RNAi-mediated downregulation of Livin expression can lead to potent antitumor activity and chemosensitizing effects in human cancers.