Diabetes mellitus (DM) is a metabolic disorder resulting with many different complications including soft tissue abnormalities in the oral cavity such as periodontitis and salivary and taste dysfunction. Previous studies also reported fungal and bacterial infections in oral cavity in these patients. This study aims to represent three dimentional morphologic ultrastructural changes of the diabetic rat tongue via scanning electron microscopy. Twenty-four (24) adult male Spraque-Dawley rats, (weight ranging between 200-250g) included in the study were randomly assigned into two groups: control rats were injected with intraperitoneally saline alone, experimental diabetes group received streptozotocin (STZ) (80mg/kg) administrated intraperitoneally. On month four, by the end of experimental period, all animals of each group were anesthetised. All tongues were dissected totally, postfixed in 2% osmium tetroxide and then dried by critical point drying before SEM analysis. Finally, superficial epithelial configurations of the lingual papillae in experimental diabetic rats were examined by scanning electron microscopy. Diabetes mellitus caused thickness, hyperceratosis and different epithelial changes, We observed yeast-like structures and bacterial colonisations on the papillar and epithelial structure of the tongue. The morphological atrophic changes of lingual mucosa and the median rhomboid glossitis (which is primary finding of candidal infection) are characteristic observations on the lingual mucosa of the streptozotocin treated rats.