Central adenocarcinoma of the jaws is an extremely rare malignant tumor. We reported a case of poorly differentiated adenocarcinoma occurring intraosseously in the maxilla. A 62-year-old male was referred to our hospital because of swelling of the palate. MRI showed a central tumorous lesion in the maxilla. He underwent maxillectomy combined with neck and parapharyngeal dissection. Histologic examinations of the surgical specimen revealed poorly differentiated adenocaricinoma showing a positive reaction for PAS, CEA and cytokeratin. He underwent adjuvant chemotherapy with cis-platinum diamminodichloride, 5-fluorouracil, and pirarubicin, but he died of multiple distant metastases 7 months after the surgery.