Traditionally, mistletoe is known as an effective anti-cancer medicinal plant, and lectin is recognized as a major component with cytotoxic and immuno-stimulant activity in mistletoe. A Korean mistletoe lectin (KML) has specificity to galactose and galactosamine and is distinguish from European mistletoe lectin (EML). When we examined the concentration of lectin in mistletoe originated from five different types of host trees, the result indicate that the lectin concentration is variable depending on the host tree. Noticeably, mistletoe from chestnut tree contains ten folds higher lectins than that of an oak tree. We also tested the concentration of KML and crude extract (KM-110) of Korean mistletoe that shows 90% cytotoxicity in L5178Y-ML25 lymphoma cell. In addition, the cells show 90% and 70% viability by the treatment of two neutralizing antibodies of KML, 9H7-D10 and 8B11-2C5 neutralization effect with two monoclonal antibodies of KML, 9H7-D10 and 8B11-2C5. Therefore, the result expected that the mistletoe contain some other cytotoxic components except lectin. Finally, the production of TNF-α and IL-6 by RAW 264.7 cells stimulated with lectin free-crude extract (LFKM-110) following neutralization by 9H7-D10 monoclonal antibody shows higher than that of lectin containing-crude extract (KM-110). These results suggest that the Korean mistletoe lectin ha a great potential to be developed as therapeutic agent of cancer.