Oxidative stress in diabetes is a result of high concentration levels of glucose and fatty acids. It plays a key role in the pathogenesis of diabetes and its complications. Its pathogenic action consists, among other things, in suppressing the synthesis of insulin in pancreatic β-cells, as well as in hampering the insulin signal transmission in target cells. This action contributes to the development of insulin resistance and induces changes in vascular walls, thus, causing diabetic complications. It was found that some antioxidants had anti-diabetic activity, for example: vitamin E, carotenoids, and various polyphenols. Medical plants used by folk medicine in different world regions have antioxidative features, and, therefore, many of those plants show anti-diabetic activity.