Objectives : Oldenlandiae Diffusae herba has been used as a natural drug for tumor, inflammation and liver disease in traditional medicine. This study was performed in order to investigate the antioxidative effects of Oldenlandiae Diffusae herba methanol extract(ODHM) on acetaminophen induced acute liver injury in mice. Methods : In order to investigate the protective effect of ODHM on acute hepatic injury in vivo, ICR mice were pretreated with ODHM, and then treated with acetaminophen(500mg/kg). And the levels of LPO and glutathione(GSH), antioxidative enzyme activities were measured. The levels of LPO were measured by TBA method. And catalase activity was measured as the decrease in hydrogen peroxide absorbance at 240nm on spectrophotometer using 30mM hydrogen peroxide. Superoxide dismutase(SOD) was assayed by recording the inhibition of nitro blue tetrazolium reduction with xanthine and xanthine oxidase. Glutathione peroxidase(GPX) activity was determined by the modified coupled assay developed by Paglia and Lawrence. The reaction was started by addition of 2.2mM hydrogen peroxide as substrate. The change in absorbance at 340nm was measured for 1min on spectrophotometer. Glutathione-S-transferase(GST) activity was assayed with CDNB as substrate and enzyme activity of GST towards the glutathione conjugation of CDNB. And Total SH and GSH levels were measured. Results : In vivo study, LPO levels of acetaminophen treatment group were significantly higher than other groups. This increased level was significantly reduced by ODHM pretreatment. The acetaminophen treatment resulted in a decrease of catalase, GPX, SOD and GST activities. By contrast, ODHM pretreatment markedly increased compare to those of untreated groups. Total SH and GSH levels were reduced by of acetaminophen treatment, and ODHM pretreatment significantly increased GSH levels.