Morus nigra (mulberries) are all widespread in Pakistan, Iran, India, and Afghanistan, where the tree and the fruit are known by the Persian-derived names king's or "superior" mulberry. Herbs are rich sources of natural antioxidants, which are used to cure many diseases in traditional medicine. The researches have shown that some herbal extracts have anti-diabetic effect, so they can be used to lower blood sugar in people with diabetes. 27 male adult rats were randomly selected and divided into three groups as nondiabetic control; diabetic control; diabetic rats treated with hydroalcoholic extract of Morus nigra leaf. In diabetic groups, alloxan monohydrate (100 mg/kg) was injected intraperitoneally to develop diabetes. Then the Test group received intraperitoneal injection of hydro-alcoholic extract of Morus nigra leaf (100 mg/kg). At last, glucose, cholesterol, triglyceride and HDL contents of the rats' serum sample were determined. The findings show that using hydro-alcoholic extract of Morus nigra leaf decreased glucose, cholesterol and triglyceride contents of diabetic rats' blood serum (p<0.01) and increased HDL content (p>0.05). Considering these findings, it is found that Morus nigra leaf can be effective in decreasing blood sugar and fat in diabetic people.