The prescription, Kilkyungtang (KKT), which originally consists of twelve kinds of medicinal plant materials and was used as a decoction for the treatment of malignant tumors and two modified Kilkyungtangs (KKT-1 and KKT-2), supplemented by the additional crude drug to KKT (KKT-1:Houttuyniae herba, and KKT-2:Oldenlandiae diffusae herba) were investigated on their antitumoral properties, in vivo respectively. All KKTs were found to exhibit significant life time-prolonging effects when they were administered orally to Sarcoma-180 bearing ICR mice for 7 days. (ILS was estimated as 20% in KKT, 42% in KKT-1 and 57% in KKT-2). A profound lessening of tumor weights was also observed when KKTs were administered to $B16-F_0$ bearing C57B/6 mice.