The cytotoxic and antitumor activity of Herba cratalariae sessiliflorae on cultured NIH 3T3 fibroblast and human oral epitheloid carcinoma cells were evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazoliumbromide (MTT) colorimetric method. The light microscopic study was carried out to observe morphological changes of cultured mouse fibroblast and human oral epitheloid carcinoma cells (KB). These results were obtained as follows; Ethyl acetate, chloroform and hexane extracts showed a significant cytotoxicity in NIH 3T3 fibroblast, but the other extracts did not show. All extracts exhibited a significant antitumor activity in human oral epitheloid carcinoma cells, but ethanol extract did not show a antitumor activity. Hexane extract showed low cytotoxic effect, but exhibited the most antitumor activity. The MTT absorbance in NIH 3T3 fibroblast was significantly decreased by treatment with chloroform, ethyl acetate and hexane extracts respectively. Human oral epitheloid carcinoma cells was significantly decreasd by treatment with all extracts with the exception of ethanol extract. The difference in MTT absorbance in two cell Types was most remarkable when treated with water and hexane extracts. Cholroform and hexane extracts showed the strongest effect in growth inhibition of human oral epitheloid carcinoma cells. These results indicated that water extract possessed no cytotoxicity and a strong antitumor activity.