Abstract: Objective 　To compare the infilt ration in melanoma models and cytotoxicity of natural killer cells activated by dendritic cells, IL-2 and IL-15. Methods 　Inoculating B16 Melanoma cells in C57BL/ 6 mice's back to establish subcutaneous models. NK cells labled by DAPI were injected via the lateral tail vein. DC, IL-2 and IL-15 were given respectively. Tumor tissues were removed at different times after injection and processed for electron microscope and fluorescence microscope. Cytotoxicity was detected by MTT assay. Results 　Cytotoxicity of NK cells cultured with DCs was enhanced. NK cells had higher cytotoxicity when N K/ DC ratio was 1∶1 than when it was 10∶1 ( P < 0. 05) . N K cells and DCs were identified through electron microscope and necrosis of target cells was observed. Infilt ration of NK cells was dose and time-dependent . More NK cells accumulated in tumors but not significantly when DCs were given compared to IL-2 or IL-15. Conclusion 　NK cells can be activated by DCs without exogenous cytotines. The activation between NK cells and DCs were related to their dose ratio.