IL-27 is a member of the IL-12 family of cytokines that is comprised of an IL-12 p40-related protein subunit, EBV-induced gene 3, and a p35-related subunit, p28. IL-27 functions through IL-27R and has been shown to have potent antitumor activity via activation of a variety of cellular components, including antitumor CD8+ T-cell responses. However, the exact mechanisms of how IL-27 enhances antitumor CD8+ T-cell responses remain unclear. Here we show that IL-27 significantly enhances the survival of activated tumor antigen-specific CD8+ T cells in vitro and in vivo, and programs tumor antigen-specific CD8+ T cells into memory precursor-like effector cells, characterized by upregulation of Bcl-6, SOCS3, Sca-1, and IL-10. While STAT3 activation and the CTL survival-enhancing effects can be independent of CTL IL-10 production, we show here that IL-27-induced CTL IL-10 production contributes to memory precursor cell phenotype induction, CTL memory, and tumor rejection. Thus, IL-27 enhances antitumor CTL responses via programming tumor antigen-specific CD8+ T cells into a unique memory precursor type of effector cells characterized by a greater survival advantage. Our results have important implications for designing immunotherapy against human cancer.