An osteofibroma is a benign neoplasm arising from the diploe of the membranous bone and is a mixture of fibrous tissue and new bone trabeculae. The tumor occurs most often on superior maxilla and the mandible. We experienced a case of osteofibroma arising from right maxillary sinus. This 42 years old female had been suffered from slowly growing mass with slight pain on her right cheek for these 2 years. On admission, Caldwell-Luc's operation was atempted under the impression of maxillary cyst, but elevating the upper lip, a large bony hard kidney shaped tumor mass with a size of about 4 by 5.5cm was encountered. After confirmation of the tumor as being osteofibroma by frozen section, the tumor mass was removed out extending the operation field.