Diabetes mellitus is a serious worldwide metabolic disease, which is accompanied by hyperglycaemia and affects all organs and body system. Zinc (Zn) is a basic cofactor for many enzymes, which also plays an important role in stabilising the structure of insulin. Liver is the most important target organ after pancreas in diabetic complications. In this study, we aimed to investigate the protective role of Zn in liver damage in streptozotocin (STZ)-induced diabetes mellitus. There are four experimental groups of female Swiss albino rats: group I: control; group II: control + ZnSO4; group III: STZ-induced diabetic animals and group IV: STZ-diabetic + ZnSO4. To induce diabetes, STZ was injected intraperitoneally (65 mg/kg). ZnSO4(100 mg/kg) was given daily to groups II and IV by gavage for 60 days. At the end of the experiment, rats were killed under anaesthesia and liver tissues were collected. In the diabetic group, hexose, hexosamine, fucose, sialic acid levels, arginase, adenosine deaminase, tissue factor activities and protein carbonyl levels increased, whereas catalase, superoxide dismutase, glutathione-S-transferase, glutathione peroxidase, glutathione reductase and Na+/K+-ATPase activities decreased. The administration of Zn to the diabetic group reversed all the negative effects/activities. According to these results, we can suggest that Zn has a protective role against STZ-induced diabetic liver damage.