A hepatoprotective compound was isolated from the ethanolic extract of the fruits of Terminalia chebula Retz. by consecutive solvent partitioning, followed by silica gel and Sephadex LH-20 column chromatographies. The purified compound was identified as a mixture of chebulic acid and its minor isomer, neochebulic acid, with a ratio of 2:1 by spectroscopic analysis including 1D and 2D NMR and MS spectroscopy. To our knowledge, this is the first report on the protection of rat hepatocytes against oxidative toxicity by chebulic acid obtained from T. chebula Retz. This compound exhibited in vitro a free radical-scavenging activity and ferric-reducing antioxidant activity. Also, the specific ESR spectrum for the •OOH radical signals consisting of three-line ESR spectra was within the field of 0.27 mT, whereas 2.5 and 0.25 mg/ml of chebulic acid significantly reduced the signal intensity of the ESR spectra to 0.06 mT and 0.11 mT, respectively. Using isolated rat hepatocyte experiment, we demonstrated that the treatment of hepatocytes with chebulic acid significantly reduced the tert-butyl hydroperoxide (t-BHP)-induced cell cytotoxicity, intracellular reactive oxygen species level, and the ratio of GSSH, oxidized form of glutathione (GSH) to the over total GSH (GSH + GSSG) (4.42%) as compared to that with t-BHP alone (8.33%).