In the study, we aimed to show the effects of vitamin B12 on the necrosis caused by methotrexate (MTX), a folic acid antagonist. Thirty-two rats were randomly assigned to four groups of eight rats per group. Control (n= 8), Vit B12 (n= 8) 3 mu g/kg/ip B12 (15 days) per day throughout the experiment, MTX (n= 8) injected with a single dose of 20 mg/kg/ip MTX on 8th day of experiment, MTX + Vit B12 (n= 8) injected with a single dose of 20 mg/kg ip methotrexate on 8th day of experiment + 3 mu g/kg/ip Vit B12 (15 days) per day throughout the experiment. Oxidant (TOS)/antioxidant (TAS) system, TNF-alpha and TGF-beta levels, AST and ALT, serum vitamin B12 levels were determined in the tissue. Cyclooxygenase-2 (Cox-2), receptor-interacting protein kinase 1 (RIP1) and 3 (RIP3) immunohistochemistry were applied to the liver tissue. TOS increased; TAS decreased; TNF-alpha and TGF-beta levels increased; AST and ALT levels changed after MTX hepatotoxicity. Vit B12 decreased significantly. COX-2, RIP1, and RIP3 immunoreactivity increased. Vit B12 showed improvement in all of the negative results. Vit B12 is an important supplement to be used against necrosis in tissue after MTX hepatotoxicity.