To observe the changes of phenotype, proliferation activity and cytotoxicity of CIK(cytokine induced killer) cells after co-culturing with dendritic cells(DCs), DCs and CIK cells were generated, respectively, by cytokines induction of culturing PBMC of healthy blood donor. The typical DCs and DCs pulsed by A549 lung cancer cells lysate antigen were co-cultured with CIK cells, respectively. Cell surface markers were analyzed by FACS method. IFN-gamma and IL-12 secreted by CIK cells and co-cultured cells were detected by ELISA. The cytotoxicities of effective cells on A549 cells and BEL-7404 cells in vitro were measured by MTT assays. The results showed that co-culture of DCs with CIK cells produced a new cell population, whose proliferation activity and cytotoxicity were much higher than CIK cells. The co-culture stimulated the maturation of DCs. The co-culture of CIK cells and A549 cells lysate antigen pulsed DC resulted in an enhanced killing activity to A549 cells than CIK cells and un-pulsed DC-CIK cells(p < 0.05). In conclusion, CIK cells co-cultured with DCs are more powerful than CIK cells alone in anti-tumor reaction.