Introduction and aim. Indo is widely one of the non-steroidal anti-inflammatory drugs and one of the common toxic effects of this drug is hepatic failure. Thymol is a monoterpene phenol with many different pharmacological activities. However, up to now its hepatoprotective effects on Indo-induced gastric ulcer model in rats have not been explored yet. Material and methods. Thirty five Sprague-Dawley rats were divided into seven groups: control, ulcer control (30 mg/kg Indo), Indo + reference standard (50 mg/ kg Rantidine), Indo + Thymol (75, 100, 250 and 500 mg/kg) groups. 10 minutes after the induction of ulcer with Indo; Thymol was orally administered to the rats. Liver function enzymes (AST, ALT and LDH) were measured from serum samples. TOS/TAC, TNF-alpha and PGE(2) levels, eNOS and Caspase-3 activity were assessed from tissue homogenate samples. In addition, histopathologic analysis on liver sections was performed. Results. Indo significantly increased the levels of hepatic enzymes, TNF-alpha and eNOS, and caspase-3 activation, while decreased PGE(2) levels. Furthermore, it induced oxidative stress as evidenced by elevated TOS and decreased TAC levels. However, Thymol treatment induced a significant improvement in these parameters, especially in 250 mg/kg dose. On the other hand, treatment with Thymol 500 mg/kg dramatically affected the parameters much worse than the Indo treated group. Conclusion. The findings of the current study demonstrated that Thymol administration significantly ameliorated liver injury due to Indo toxicity. This effect of Thymol (250 mg/kg) may be mediated by its anti-oxidative or anti-inflammatory effect, and up-regulation the synthesis of PGE(2).