The abundantly available source of stem cells and the low incidence of graft-versus-host disease (GVHD) made cord blood an attractive alternative source of hematopoietic stem cells for transplantation. Besides T cell and NK cell, NKT cell played an important role in low incidence of GVHD during allogeneic transplantation. IL-2 and IL-15 can stimulate T cell and NK cell proliferation, survival and activation in vitro. But they exhibited different effects on the GVHD during allogeneic transplantation. In this study, we explored the different effects of exogenous IL-2 and IL-15 on the expansion of CD3+CD56+ NKT-like cells by in vitro long term culture of cord blood mononuclear cells (CBMCs). The results showed that CD3+CD56+ NKT-like cells were derived from CD34−CD56− CBMCs and IL-2 improved CD3+CD56+ NKT-like cell expansion more strongly than IL-15. Interestingly, CD3+CD56+ NKT-like cells from IL-15-cocultured CBMCs had significantly lower apoptotic frequency and higher levels of activation markers (CD161, CD25, and IFN-γ) than those from IL-2-cocultured CBMCs. The anti-apoptotic and activating effects of IL-15 on CD3+CD56+ NKT-like cells from CBMCs might possibly explain the pathogenic role of IL-15 in GVHD during allogeneic transplantation.