The aqueous extract of Terminalia arjuna bark was investigated for its hepatoprotective effect against isoniazid induced acute liver damage on albino rats. Isoniazid (100mg/kg) significantly elevated the serum levels of biochemical markers like SGPT, SGOT, ALP, ACP, Bilirubin, Protein and depleted antioxidant enzymes GSH and SOD upon administration of Isoniazid (100mg/kg) to albino rats. This indicated that there the aqeous extract of bark of Terminalia arjuna at 200mg/kg dose significantly reduced the elevated levels of biochemical markers mentioned above. Test extract treatment also increased the level of SOD and GSH. These results suggest that aqueous extract of Terminalia arjuna may have the potential therapeutic value in the treatment of Isoniazid induced hepatic damage and some liver diseases. Hepatoprotective activity of the study plant may be attributed to the anti-oxidant principles in it.