Effects of Korean mistletoe extracts (KM-110), Viscum album coloratum on the specific and non-specific immune responses of Japanese eel Anguilla japonica were examined. The optimal concentration not showing toxicity of KM-110 was determined to $30-40{mu}g/ml$ in vitro and $100{mu}g$/100 g of fish in vivo. Even $1000{mu}g$ of KM-110/100 g of fish did not show any clinical problem in fish though the levels of toxic parameters were slightly increased. In terms of antibody production, KM-110 significantly elicited more antibody production than FCA or $eta$-glucan. $eta$-glucan plus KM-110 group synergistically enhanced antibody production. There was no significant difference between KM-110 and KM-110 plus $eta$-glucan group. The ROI production by head kidney (HK) leucocytes of eel injected with 500 or $1000{mu}g$ KM-110 was significantly (P<0.05) enhanced than the control and FCA-treated group. Maximum increase in the NBT reduction value was observed in $1000{mu}g$ KM-110 group but no significant difference was found between 500 and $1000{mu}g$ KM group. The level of serum lysozyme activity was significantly (P<0.05) higher in the 500 and $1000{mu}g$ KM-110- or FCA-treated group than in the control and $200{mu}g$ KM-110 group. The phagocytic activities of HK leucocytes isolated from eel injected with 500 and $1000{mu}g$ KM-110 were significantly (P<0.05) higher than $200{mu}g$ KM-110 and PBS-injected control group. Korean mistletoe appeared to be a good activator of the specific and non-specific immune responses of Japanese eel.