Lichens can be used as a novel bioresource for natural antioxidants. However, there is need for further investigations to validate the lichens used in medicinal remedies. In this study, the effects of Cetraria islandica and Pseudevernia furfuracae lichen species in streptozotocin (STZ)-induced diabetes were evaluated. Diabetic rats were treated with aqueous lichen extracts (250 and 500 mg/kg/day) for 2 weeks starting at 72 h after STZ injection. On the 14th day, animals were anesthetized, and then metabolic and biochemical parameters were evaluated between control and treatment groups. Pancreatic histology and -cell mass were examined by hematoxylin and eosin and insulin immunohistochemistry stainings. Our findings revealed that these lichen species could be used safely in this dose range. In addition, C. islandica extracts showed prominent results compared to the doses of P. furfuracae extract for antioxidant capacity. However, the protectivity of C. islandica extract was inadequate against diabetes-induced pancreatic damages via forming oxidative stress. In conclusion, the usage of C. islandica might serve for early intervening in the risk reduction of type 1 diabetes.