Exposure to thioacetamide causes hepatotoxicity and hepatocellular carcinoma in human, while fish oil Omega-3 supplement has anti-inflammatory effects. In this study, the protective effect of Fish oil Omega-3 supplement against liver-related biochemical factors changes induced by thioacetamide in rat is investigated.42 male rats were divided into 6 groups of seven. The control group, The sham 1 group receiving 0.4ml/kg olive oil as the solvent of Fish oil Omega-3 supplement, the sham2 group inter peritonealy receiving a dose of 150 mg/kg thioacetamide at the end of the experiment, the experimental groups 1, 2 and 3 orally receiving a daily dose of 100, 200 and 300 mg/kg Fish oil Omega-3 supplements respectively for 3 month followed by an inter peritoneal dose of 150 mg/kg thioacetamide at the end of the experiment. The serum levels of GGT, LDH, albumin and total protein were measured. Following hematoxylin-eosin staining, liver tissue samples were pathologically studied.The mean level of Albumin showed a significant reduction in experimental groups 1, 2 and 3 receiving thioacetamide. Also, the mean concentration of GGT In the experimental groups 1 and 2 compared to the group receiving thioacetamide decreased significantly; whereas, the mean levels of LDH and total protein showed no significant changes in the experimental groups 1, 2, and 3 (pd"0.05). The results of this study indicate that Fish oil Omega-3 supplement has a protective effect on liver-related biochemical factors changes induced by thioacetamide in rat.