PURPOSE: To provide an antitumor agent containing SAIKO saponin as an active component, having extremely low toxicity, free from hemolytic action and having antitumor action and carcinostatic action.

CONSTITUTION: SAIKO saponin existing in SAIKO (a Chinese herb drug) such as MISHIMA-SAIKO (Bupleurum falcatum L.) or HOTARU-SAIKO (Bupleurum longiradiatum T.) is used as an active component of the titled antitumor agent. SAIKO saponin can be produced by the extractive separation and purification of SAIKO or hydrolyzing the saponin with an acid, alkali or enzyme. The above saponin component has low toxicity and exhibits antitumor activity. It is effective against almost all tumors such as hepatic carcinoma, dermatic carcinoma, uterine carcinoma, gastric carcinoma, sarcoma, etc. Dose: about 50W500mg of saponin component daily by oral administration.