We attempted to isolate and characterize the lectins from stem and leaves of Korean mistletoe (Viscum album var.coloratum) by affinity chromatography. Lectin I was isolated only from stem. Lectin II was not isolated from Korean mistletoe, whereas lectin III was isolated from the stem and leaves. The hemagglutinating activity of lectin I was 16HU and inhibited by D-galactose, lactose, and N-acetyl-D-galactosamine. The lectin I has molecular weight of 60,000D being composed of two basic subunits with molecular weights of 32,000 D and 28,000 D which are linked by a disufide bond. The lectin III from stem has molecular weight of 66,000D being two basic subunits which have molecular weights of 34,000D and 29,000D and are linked by a disufide bond. The activity of lectin I was stable at the pH range of 4.00 approximately 8.50, and at a wide range of temperature (0 approximately 42 degrees C). The lectin I showed more potent mitogenic activity to murine lymphocytes than concanavalin A.