An ulcer is defined as loss of epithelium. Although many oral ulcers have similar clinical appearances, their etiologies encompass many disorders, including trauma, infection, immunologic disease, and malignant oral cancer. Oral squamous cell carcinoma(SCC) occupying about 90% of oral cancer, usually manifests as unhealed ulcer over 2 weeks. Oral SCC can metastasize to the cervical neck lymph node, and therefore the surgical therapeutic modality for oral SCC could encompass the neck node dissection as well as wide excision for primary lesions, which should leave the post-operative complication of functional damage like dysphagia and facial deformity. Therefore, it is important to discriminate oral SCC from other ulcerative conditions to make a prompt management. The knowledge for the pathogenesis of the ulcerative lesions could help the clinicians to understand the differences of clinical features and to practice an appropriate therapeutics.