Tongue cancer is one of the most prevalent malignancies in oral and maxillofacial area.Early diagnosis is crucial for improved clinical outcome. Regarding malignant transfor mation, it is important to understand the concept of oral potentially malignant disorders and oral epithelial dysplasia (OED). We present two cases of oral squamous cell carci noma (OSCC) developing from OED on ventral tongue. Both of our cases progressed from mild OED to moderate OED, and then severe OED, eventually resulting in OSCC. Our cases underscore that clinicians must look into pathological description of epithelial dysplasia, not only clinical diagnosis of the lesion. Clinical features such as indurated nodules, a mixed white and red appearance, and thick verrucous plaques were closely monitored, enabling the prompt detection of OSCC through biopsy of the relevant site.