Hwanhonsan has been used for curing tumor as a Oriental medicine without any experimental evidence to support the rational basis for their clinical use. This experiment was carried out to evaluate the possible therapeutic or antitumoral effects of Hwanhonsan extract against cancer, and to study some mechanisms responsible for its effect. Some kind of tumors were induced by the typical application of 3-methylcholanthrene(MCA) or by the implantation of malignant tumor cells such as leukemia cells(3LL cells) or sarcoma cells(S180 cells) and FasII cells. Treatment of the Hwanhonsan extract(daily 1 mg/mouse, i.p.) was continued for 7 days prior to tumor induction and after that the treatment was lasted for 20 hrs. Against squamous cell carcinoma induced by MCA, Hwanhonsan decreased. not only the frequency of tumor production but also the number and weight of tumors per tumor bearing mice(TBM). Hwanhonsan also significantly suppressed the development of 3LL cells and S180 cells implanted tumors by frequency and their size, and some developed tumors were regressed by the continuous treatment of Hwanhonsan extract into TBM. However, when tumor was induced by FsaII cells implantation, the growth of implanted cells in mice was delayed by the water extract of Hwanhonsan until 7 days and then rapid growth ensued. In vitro treatment of Hwanhonsan extract had no inhibitory effect on the tumor induced by some kind of cell lines such as A431 cells strain but it significantly inhibited the proliferation of 3LL cells, S180 cells. These results suggested that Hwanhonsan extract exhibited a significant prophylactic benefits against tumors and its antitumor activity was manifested depending on the type of tumor cells.