Diabetes mellitus is the most common endocrine disorder and a major cause of morbidity and mortality. Traditional medicines worldwide suggest a wide range of natural remedies for the prevention and treatment of chronic disorders, including diabetes mellitus. This mechanistic review aims to highlight the significance of medicinal plants traditionally used as dietary supplements in Persian medicine in adjunct with restricted conventional drugs for the prevention and treatment of diabetes mellitus. Mounting evidence suggests that these natural agents perform their protective and therapeutic effect on diabetes mellitus via several cellular mechanisms, including regeneration of pancreatic β cell, limitation of glycogen degradation and gluconeogenesis, anti-inflammatory, immunoregulatory, antiapoptosis, antioxidative stress, as well as modulation of intracellular signaling transduction pathways. In conclusion, traditional medicinal plants used in Persian medicine can be considered as dietary supplements with therapeutic potential for diabetes mellitus and maybe potential sources of new orally active agent(s).