The cytotoxic and antitumor activity of Perilla frutescens extract on cultured 3T3 fibroblast and skin melanoma cells were evaluated by tetrazolium MTT (MTT) and neutral red (NR) colorimetric assay methods. Lactate dehydrogenase activity was also measured. The light microscopic study was carried out to observe morphological changes of cultured mouse fibroblast and skin melanoma cells. The results were as follows: 1. Water and ether extracts showed a significant cytotoxicity in 3T3 fibroblast and all extracts exhibited a significant anti-tumor activity in skin melanoma cells. Methanol, ethyl acetate and ethanol extracts showed low cytotoxic effects, but exhibited a high anti-tumor activity. 2. The MTT absorbance in 3T3 fibroblast was significantly decreased by treatment with ether, water, chloroform and ethanol extracts and skin melanoma cells was significantly decreased by treatment with all extracts. The difference in MTT absorbance in two cell types was most remarkable when treated with methanol and ethanol extracts. 3. Methanol and ethyl acetate extracts showed the strongest effect in growth inhibition of melanoma cells. These results indicated that methanol extract possessed a low cytotoxicity and a strong anti-tumor activity.