In order to investigate the immunity of unloaded dendritic cells (DCs) derived from murine bone marrow to preexisting lung melanoma metastases of mice, MO5 were intravenously injected to induce lung metastases in syngeneic C57BL/6 mice. Unloaded GM-CSF DCs, PBS and DCs+SIINFEKEL were subcutaneously injected into the mice, which were divided as experimental group, negative control group and positive control group respectively. Monoclonal antibody was used to deplete NK or T cells separately. The immunity-inhibitory effects on the lung melanoma were observed and the corresponding effector cells were examined. It was found that in the experimental and positive groups, the regression was induced in metastatic nodules in the lungs of tumor-bearing mice,but abrogated by treatment with anti-asialo-GM1 but not anti-CD8. It was concluded that the unloaded DCs could suppress the lung melanoma metastases to some extent, which was mediated by NK cells, and could be used as a potent therapeutic agents for lung tumor.