The toxicity and antitumour effect of the ethanol extract of Selaginella tamariscina (STE), a plant widely used in folk medicine, were examined in a mice model. In the single-dose acute toxicity test, an oral administration of 10,000 mg kg(-1) STE did not cause any lethality. The sub-acute toxicity study showed that the treatment by 250, 1000 and 3000 mg kg(-1 )day(-1) for 30 continuous days did neither alter the body weights nor the haematological parameters in BALB/c mice. The anticancer effect of STE was evaluated in BALB/c mice inoculated with Lewis lung carcinoma cells. Oral administration of STE could not prevent the tumour formation but provided strong inhibition of tumour growth.