Objective : It is well known that Gagamsojeokbackchool-san show antitumor effects and its activities are result from enhancement of immune function, we investigated the antitumor effects of Sambonggangyongbaneo-tang and its mechanism. Methods : We measured change of body weight, weight of immune organs (Spleen, Thymus), Liver, Kidney, tumor weight, cytotoxicity for investigation of antitumor effects of Sambonggangyongbaneo-tang. Results : 1. The body weight of mouse has no significant difference between control and sample groups. 2. The weights of immune organs (Spleen and Thymus) decreased significantly in sample groups. The weights of Liver and Kidney have no significant difference. 3. The tumor weights in mouse decreased significantly in sample groups and showed dose-dependent effect. 4. Cell viability of Sarcoma 180 has no significant difference in sample groups. 5. HeLa cell viability has no significant difference in low concentration, but it decreased significantly in high concentration. Conclusions : According to the above results, it could be suggested that Sambonggangyongbaneo-tang has prominant antitumor effects and cytotoxicity.