Oral galvanism is known to induce chronic irritation on oral mucosa, but the related pathology rarely occurs. A 65 years old male complained of linear horizontal ulcerations on his bilateral buccal mucosa for one month. The oral ulcerations were parallel and approximated to his occlusal plane. He had multiple metallic crowns using gold and nickel cobalt alloy at bilateral upper and lower molar teeth, and also had accustomed to heavy smoking for more than twenty years. Biopsy examination was performed with immunohistochemical staining using antisera of PCNA, D2-40, and PARP. The epithelial ulcer had clear margin and was replaced by granulation tissue containing many dilated lymphatic vessels, which were positive for D2-40, but showed no feature of pseudo-necrotic membrane. Nearby epithelium showed the typical features of leukoedema, characterized by edematous keratinocytes with clear cytoplasms and pyknotic nuclei, low rete ridges, and rough superficial epithelial layer, where PCNA was rarely positive. Some superficial edematous keratinocytes showed perinuclear cytoplasmic vacuolization, and their peripheral nuclear chromatins were positive for PARP. Taken together, the present mucosa ulceration was different from aphthous stomatitis, herpes stomititis, oral lichen planus, etc., thus it was postulated that the galvanic current generated from between the upper and lower dissimilar metal crowns could affect the precedent leukoedema caused by heavy smoking habit and produce the linear horizontal buccal ulceration. Therefore, the present case was diagnosed as galvanic mucositis associated with leukoedema, and it was also hypothesized that the mild and persistent galvanic current was able to deplete the cytoplasmic fluid of leukoedema keratinocytes via the osmotic pressure difference elicited by increased ionic concentration of galvanism, and followed by severe keratinocyte apoptosis and oral mucosa ulceration.