Mistletoe (Viscum album) is a common name for many species of semi-parasitic plants which grow on deciduous trees all over the world. In this study, the immunomodulatory activity of the water-extract of Korean mistletoe fruits (KMFWE), was investigated on murine peritoneal macrophages. The culture supernatants of KMF-WE-stimulated murine peritoneal macrophages showed the increased production of IFN-$gamma$, IL-$1{eta}$ and TNF-$alpha$, in a dose-dependent manner. KMF-WE also induced chemokine production from murine peritoneal macrophages such as RANTES, MCP-1, MIP-$1{alpha}$ and MIP-$1{eta}$, as well as nitric oxide (NO) production, in a dose-dependent manner. The gel filtration fraction revealed F-1, which is the early-eluted and high molecular weight product, is the major fraction of KMF-WE to activate the murine peritoneal macrophage to induce cytokines, chemokines and NO. The nature of F-1 fraction needs to be examined in detail in further studies to define the regulatory mechanisms of cytokine or chemokine induction by KMF-WE on macrophages. These results suggest that KMF-WE possess a potent immunostimulant activity and can be a promising candidate available for development of immunomodulators.