Objective : The present study was carried out to investigate the effects of NaisoOkseol-Tang (NOT) on solid tumor in mice in terms of immune-potentiating and direct cytotoxic action of NOT in vitro and vivo study. Methods: The present author investigated thymocyte proliferation and NO production to confirm immune-potentiating activity of NOT and also investigated body/tumor weight and survival rates in tumor bearing mice. In this study, administration of NOT decreased tumor/weight ratio significantly, and prolonged survival duration compared to non-treated control. Treatment with NOT also elevated proliferation rates of thymocytes isolated from tumor bearing mice. Results: In vitro study, treatment with NOT suppressed proliferation rate of Sarcoma 180 (S-180) cells. Contrary, treatment with NOT elevated proliferation rate of thymocytes. These results were co-related with in vivo study. In addition, NO production from abdominal macrophages isolated from normal mice was not affected by treatment with NOT. Conclusion : NOT is useful to treat patient with solid tumor, because NOT has direct toxic action for tumor cell and immune-potentiating action for T cells.