Protective effect of Corydalis ternata against the carbon tetrachloride-induced toxicity was investigated. Carbon tetrachloride(CCl₄) induces hepatotoxicity due to the reactive free radical(CCl₃*) generated by cytochrome P-450 enzyme. We examined effects of hexane, chloroform, butanol and water fractions prepared from the Corydalas ternata methanol extract. Rats were treated with those for 3 days, and liver microsomes and cytosols were prepared at 24 hour after last treatment. Hepatoprotective activity. of the water fraction was higher than that of other fractions. To examine mechanism of the hepatoprotective effect of Corydalis ternata, we measured contents of malondialdehyde(MDA), cytochrome P450(CYP), glutathione, calcium as well as the activities of NADPH-CYP reductase, glutathione S-transferase(GST), superoxide dismutase(SOD), glutathione peroxidase(GPX) and catalase. The fraction inhibited production of MDA, content of CYP and calcium in liver of water fractions - treated rats as compared with those of CCl₄ treated rats. The GST activity was increased. We speculate that the O₂ radical scavenging activities of the water fraction might play a key role in the mechanism opposing the progression of CCl₄ induced hepatotoxicity, but the activities of SOD, GPX, CAT were decreased. These results suggest that the mechanism might be mainly due to the decrease of CYP contents, act as calcium channel Mocker and increase of GST activity rather than O₂ radical scavenging activities.