Adenosquamous carcinoma (ASC) of the head and neck is extremely rare. We experienced ASC of the mandibular gingiva in a 64 year-old man having a history of lobectomy for pulmonary adenocarcinoma. The patient visited our clinic complaining of painless swelling on the mandibular gingiva in the central, lingual region. Soft, relatively smooth tumor measured 2.5×1.5cm in diameter was found on the gingiva. The overlying mucosa was deeply hyperemic and erosive in parts. One of the left submandibular lymphnodes solidly swelled to the size of the thumb-tip. Biopsied specimens exhibited both natures of squamous and adenomatous carcinoma microscopically, and the tumor was extirpated with no induction therapy. Histopathologic findings of the extirpated lesion were those of tumor nests consisted of proliferated peripheral basaloid cells and central squamous cells with necrotic spaces which gave a pseudoglandular picture. In some areas, mucous substance was observed in the ductlike structure, and mucous cells could be identified though being only few in number. Immunohistochemically, it was found that Total-Keratin was positive in the whole tumor cells, but RGE-53 Keratin existed only in basaloid cells. Metastatic lymphnode exhibited almost the same appearance as the primary lesion. From the above findings, the gingival tumor was considered as ASC but not a metastatic lesion from lung adenocarcinoma.