Korean mistletoe (Viscum album) extract has been found to posses immunostimulatory activity. In this study, Korean mistletoe extract, M11C (non-lectin components), was used to know whether this extract might activate mouse splenic macrophages to produce tumor necrosis $factor-{alpha};(TNF-{alpha}$) and might play a role in anticancer. To know the effect of M11C on the production of $TNF-{alpha}$, the splenic macrophages were treated by the M11C, and then collected the supernatant (M11C stimulated splenic macrophage-conditioned media; MSCM). MSCM was analyzed for the $TNF-{alpha}$ secretion by means of ELISA and immunoblotting, and mRNA expression was analyzed by RT-PCR. The S-180 murine sarcoma model was established to know the effect of M11C on the inhibition of tumor growth. M11C had the effect of $TNF-{alpha}$ production from splenic macrophages performed by ELISA technique. This ELISA data was reconfirmed by immunoblotting assay. The effects of M11C on the expression of $TNF-{alpha}$ mRNA from the macrophages was also shown. M11C also had the inhibitory effect of S-180 tumor growth. These data suggest that Korean mistletoe extract M11C may be used for an immunomodulator.