Use of a tongue flap has been advocated for the treatment of various defects in the mouth, and application for the closure of extended oro-nasal fistulae is widespread because of its rich blood supply. We report herein closure of an oro-antral fistula after partial maxillectomy using a laterally based tongue flap.A 63-year-old man was diagnosed as upper gingival carcinoma. Partial maxillectomy was performed under general anesthesia. After the operation, maxillary defect was sealed with partial denture. About 5 years postoperatively, the patient complained of an unpleasant feeling of the partial denture. Closure operation was performed under general anesthesia. A tongue flap was raised from the dorsum of the tongue including mucosa and underlying muscle, based laterally. The tongue flap was turned upward and the tip was sutured to the lateral edge of the maxillary defect, then the base was sutured to the middle of the maxillary defect. The flap was well vascularized and necrosis of the flap did not occur. Five months postoperatively, the oro-antral fistula was kept completely closed. Therefore, closure of the oro-antral fistula using a tongue flap is useful for medium-sized maxillectomy defects.