The study has shown that the cytotoxity of ethanol-extract from the root and rhizome of Rheum of ficinale is very low. It shows no cytotoxity even at 20,000 micrograms/ml and on the contrary tends to promote cell growth. Obvious anti-viral action can be observed in cell culture. The minimum inhibition dose for herpes simplex virus (HSV) is 100 micrograms/ml. Also, the extract helps to prevent cells from viral infections and has some direct effect on viral particles.