Methotrexate is used as a chemotherapeutic agent and its anti-oxidant activity is used to treat many cancer types. This study conducts a biochemical and histopathological investigation into whether mirtazapine has a protective effect on methotrexate-induced hepatotoxicity in rats. Distilled water was given to a healthy group intraperitoneally. Methotrexate alone was injected in the control group, again intraperitoneally. Mirtazapine and, 1 h later, methotrexate were given to the rats in the final group. This procedure was repeated over 7 days. In the control group rats receiving methotrexate, blood AST, ALT, and LDH levels were 227±3 μmol/l, 85±2 μmol/l, and 357±13 μmol/l, respectively. In the rats receiving mirtazapine and methotrexate, these values were 152±3 μmol/l, 25±1 μmol/l, and 141±15 μmol/l. In the healthy rat group, AST, ALT, and LDH levels were 136 μmol/l, 20 μmol/l, and 133 μmol/l, respectively. Histopathologically, apoptotic bodies with condensed cytoplasm, peripheral, and pyknotic nuclei in the hepatocytes, focal necrosis and intense inflammation in the interstitial areas were present in the control group. In the methotrexate and mirtazapine group, there were no apoptotic bodies or inflammation, only isolated necrosis in the hepatocytes. In conclusion, mirtazapine protected the liver against methotrexate toxicity.