Malignant melanoma is a highly malignant tumor derived from melanocyte. Malignant melanoma of the oral cavity occurs mainly in the palatine mucosa and the maxillary gingiva in men in their 50s. Malignant melanoma can be divided into pigmented and non-pigmented(amelanotic). Among them, non-pigmented malignant melanoma accounts for 2-8% of all malignant melanomas. Pigmented malignant melanoma is detected through changes in pigmentation, whereas non-pigmented malignant melanoma is characterized by no pattern of color change. In this study, at the initial visit, a malignant lesion was suspected and a biopsy was performed. According to the biopsy results, it was diagnosed as polymorphic sarcoma, but the histological examination performed during the operation revealed that it was amelanotic melanoma. As such, the differential diagnosis is important because there is no clinical change in non-pigmented malignant melanoma. Diseases to be differentially diagnosed when non-pigmented malignant melanoma occurs in the oral cavity include squamous cell carcinoma, lymphoma, sarcoma, inflammation, and osteomyelitis. In this study, we report a case that showed the histopathological characteristics of malignant melanoma without superficial pigmentation.