Natural killer cell (NK) is known as a major immune system in body through mediating cell death via several possible pathways, and one of three subpopulations of lymphocytes functioning as scavenger of tumor, virus infected cells etc. Our present results found that the SOD-contained silkworm larvae powder caused an enhancement of the effect on NK cell cytotoxicity, which implied this material modulated the immune system in mice in vivo. The NK cell activities of S180 tumor modeled mice treated with silkworm powder including SOD were enhanced significantly ranging from 30% to 48%, respectively, compare to a distilled water feeding control and silkworm powder without SOD. Meanwhile, the ConA-stimulated splenocyte proliferation of all three treated groups was higher than that of the control both in T cells or B cells. The average tumor weight of S180 modeled mice treated with doses of SOD-contained silkworm powder was lighter than that of water control showing the tumor inhibition rates (IR) reached to 22.51% to 37%, respectively. In conclusion, these findings demonstrate that administration of silkworm larvae powder containing SOD results in activation of NK cells and immune T-cell and B-cell, suggesting the silkworm larvae powder containing SOD play a positive role in tumor inhibition.