||Lipid peroxidation, a general mechanism whereby oxygen free radicals indu ce tissue damage, has been implicated in diverse pathological conditions, incl uding cancer, atherosclerosis, ischemia, inflammation, irradiation, aging and so on. The present study is to investigate the lipid peroxidation inhibition of the natural products. Experiments were conduct to screen the anti-lipid per oxidation activity of Chinese medicinal herbs or natural plants. A reversed-ph ase high performance liquid chromatographic method is used for the determinati on of malonaldehyde in liver homogenates. The standard test for lipid peroxida tion is the measurement of the peak, 532nm absorbing chromogen formed upon rea ction with 2-thiobarbituric acid. This reaction depends upon the presence of t he lipid peroxidation product malondialdehyde (MDA) which reacts with 2-thioba rbituric acid (TBA) to form MDA(TBA)2 with a absorption maximun at 532 nm. Fr om this screening system, we tested water extract of Atractylodes ovata De Can dolle has the highest anti-lipid peroxidative effect. ( IC50 = 45.8 (g/ml ) Bai-Zhu ( rhizome of Atractylodes ovata De Candolle ) is one of the common to nic Chinese herbs. It has been used to invigorate the spleen and benefit vital energy. Since we found the n-hexane extract of Bai-Zhu possessed a strong ant ioxidative activity ( IC50 = 21.6 (g/ml ), we used silica gel chromatography t o isolate the antioxidative components. Four pure compounds were identified as Atractylenolide I, II, III and Atractylon, by mass and infared spectrometer a s well as their physical constant. We found the most potency in anti-lipid per oxidative activity for the four pure compounds of Bai-Zhu was Atractylon. ( IC 50 = 15.9 (g/ml ) Accordingly, we chose Atractylon as standard to quantitative analysis of Atractylon in each extraction from Chinese herbs by HPLC. The HPL C quantitative analysis conditions are as following: column: LiChrospher l00 R P-18e ( 250×4 mm I.D. ); mobile phase: CH3CN-H2O ( 80:20 ); flow rate: 1.0 ml /min; detector: UV 220 nm. We found that among the extractions of Bai-Zhu with soil baking Atractylon by n-hexane extract is the highest. ( 102.4 (g/g ). Th ese results will provide information to Chinese medicinal pharmaceutical indus try and research.